biological flora of new zealand 13. pittosporum cornifolium , tāwhiri...

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Biological flora of New Zealand 13.Pittosporum cornifolium, tāwhiri karo,cornel-leaved pittosporumFM Clarkson a , BD Clarkson a & CEC Gemmill aa Department of Biological Sciences , University of Waikato ,Hamilton , New ZealandPublished online: 26 Apr 2012.

To cite this article: FM Clarkson , BD Clarkson & CEC Gemmill (2012) Biological flora of NewZealand 13. Pittosporum cornifolium, tāwhiri karo, cornel-leaved pittosporum, New Zealand Journalof Botany, 50:2, 185-201, DOI: 10.1080/0028825X.2011.645547

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Biological flora of New Zealand 13. Pittosporum cornifolium, tawhiri karo,

cornel-leaved pittosporum

FM Clarkson*, BD Clarkson and CEC Gemmill

Department of Biological Sciences, University of Waikato, Hamilton, New Zealand

(Received 5 July 2011; final version received 15 November 2011)

A comprehensive review of the morphology, anatomy, taxonomy, chemistry and ecology of theendemic New Zealand facultative shrub epiphyte Pittosporum cornifolium (Pittosporaceae) ispresented. Strong habitat specificity restricts this species to lowland forest and coastal habitats,which are widely yet discontinuously distributed north of latitude 42815?S. Pittosporumcornifolium is typically associated with old growth forest systems and low nutrient substrates,with low mean daily temperatures in the coldest month (B0.6 8C) and high mean Octobervapour pressure deficits (�0.5 kPa) apparently restricting its distribution. Significantmorphological variability is evident in leaves and flowers, especially with respect to plants fromthe Poor Knights Islands. Genetic analyses of five mainland populations and individualsrepresenting Poor Knights Islands populations revealed relatively low genetic diversity at thepopulation level which is likely to be the result of geographic isolation. Molecular phylogeneticstudies suggest a New Caledonian origin for the species with close affinities to bothP. pimeleoides subspecies. Several lines of evidence suggest recognition of the Poor KnightsIslands entity as a new taxon. However, analysis of additional morphological, reproductive andmolecular data across the full geographic range will be required to confirm current inferences.Although populations have declined, P. cornifolium is not currently threatened, however, itshould be considered for reintroduction to sites in districts where its range has been severelyreduced.

Keywords: biological flora; epiphyte; facultative; lowland ecosystems; New Zealand;Pittosporaceae; Pittosporum cornifolium; tawhiri karo

Introduction

Pittosporum cornifolium A. Cunn. ex Hook.

(Pittosporaceae) is an endemic shrub epiphyte

that typically perches on forest canopy trees,

but also grows on the forest floor (terrestrial

lifestyle) or on rocks (rupestral). This species is

one of four shrub epiphytes endemic to

New Zealand, the others being P. kirkii,

Brachyglottis kirkii and Griselinia lucida (Oliver

1930). Pittosporum cornifolium has a distinctive

whorled leaf arrangement, reddish brown

(Hooker 1832) to yellow flowers (Cooper

1956), which are typically unisexual in function

(Petrie 1921), and capsules characteristic of the

genus with seeds embedded in a sticky pitch

substance (Gaertner 1788). The primary habi-

tats of P. cornifolium are lowland and coastal

ecosystems which, in recent times (B200 years),

have been subjected to widespread clearance

and fragmentation, resulting in major reduc-

tions to the species’ potential population range

(F.M. Clarkson 2011). Despite habitat discon-

tinuity, P. cornifolium occupies a wide geo-

graphic range which extends throughout the

North Island, including numerous offshore

islands, to the northern reaches of the South

*Corresponding author. Email: [email protected]

New Zealand Journal of BotanyVol. 50, No. 2, June 2012, 185�201

ISSN 0028-825X print/ISSN 1175-8643 online

# 2012 The Royal Society of New Zealand

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Island (Cooper 1956). Targeted scientific re-

search specific to this inconspicuous epiphyte

species has been very limited. Early morpholo-

gical and anatomical research has been re-

stricted to a few individuals from a single

geographic region (Kirk 1871; Petrie 1921;

Oliver 1930; Cooper 1956; Wilkinson 1992).

More recent research by F.M. Clarkson (2011)

highlights the morphological and anatomical

variability and genetic diversity of the species

based on a study of five North Island popula-

tions and individuals from the Poor Knights

Islands, but comparative research is yet to be

conducted more broadly across its natural

range. Basic information regarding pollination

and dispersal modes, seed viability and germi-

nation is lacking. Hence, a review of the

available biological research is presented to

summarize the current state of knowledge, but

also to highlight information gaps and encou-

rage future research which will be of value in

aiding the conservation and restoration of this

distinctive species.

Morphology

We base our morphological description on

Cooper’s (1956) work, which is the most

comprehensive description of P. cornifolium.

Pittosporum cornifolium is a perennial, ever-

green shrub reaching up to 2.5 m in height,

with a distinctive whorled architecture.

Branches are dark reddish brown, glabrous

and grow in a forked or whorled�verticillatearrangements. Leaves are simple, entire with

slightly revolute margins and grow in a

whorled arrangement. They are ciliate when

young, but soon become glabrate, coriaceous,

with a glossy cuticle and have a well-raised

midrib above (immersed below), and distinct

secondary veins below. Leaves are elliptic�lanceolate to obovate (acute to subacuminate

at apex and acute to obtuse at base), 2�10 cm

long and 1�5 cm wide. Petioles are broad and

glabrous, c. 0.5�3.0 mm long and 0.5�2.0 mm

wide. Inflorescences are terminal, 1�10 flow-

ered [depending on functional sex of flowers

(Petrie 1921)], usually umbelliform. Flowers

(Fig. 1) are a reddish brown (type form

described by Hooker 1832) to yellow in colour.

Flower pedicels are 2�15 mm long and are

subtended by a whorl of leaves with associated

caducous bud scales. Flower sepals are non-

overlapping, of narrow�lanceolate shape, acuteat apex and are 4�7 mm long. Petals are broad,

coherent in a tube basally with reflexed tips

Figure 1 Pittosporum cornifolium individuals in flower. A, Light red colouring (photo: Kerry Jones, Hauturu/Little Barrier Island). B, Reddish brown colouring (photo: Rob L. Suisted, Wilton’s Bush Reserve,Wellington). C, Yellow colouring (individual from the Poor Knights Islands).

186 FM Clarkson et al.

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apically, linear�lanceolate, acute to acuminate

at the apex, and 8�12 mm in length. Stamens

are 4�6 mm long, anthers sagittiform to

elliptic�oblong, 1�2 mm long and 0.5�1 mm

broad. Gynoecia are of similar length to sta-

mens, the ovaries are broad and covered with

villous hairs, 1.5�3 mm long and 0.5�2 mm

broad, styles are 2.5�4 mm long and stigmas

range from capitate (two-lobed) to truncate.

Petrie (1921) noted that although flowers are

perfect, they are generally unisexual in func-

tion; male flowers have robust stamens and a

withered/aborted ovary, whereas female flow-

ers have an inflated ovary and apparently

aborted stamens (Fig. 2). Capsules are two-

valved (occasionally three) with a persistent

style, c. 1 cm in diameter and ovoid to ellipsoid.

Capsule valves areB1 mm thick and have

vermilion-stained interiors. The placentae bare

thick strap-like funicles up to 5 mm in length.

Seeds are glossy, usually black and irregular

(3.1�6.5 mm long), embedded in a viscid

substance (Webb & Simpson 2001), with four

to eight seeds per capsule.Morphological variants of P. cornifolium

have been recognized previously. In comparison

with mainland (‘type’) plants, individuals from

the Poor Knights Islands have yellow flowers

(Smith 2004), and larger, thicker, more coriac-

eous leaves that are obovate to rhomboid

(subacuminate to obtuse at apex and acute to

obtuse at base) (F.M. Clarkson 2011).

Illustrations

Pittosporum cornifolium is illustrated by Hoo-

ker (1832, pl. 3161; Fig. 3), Osborne (in

Goulding 1983, pl. 35), Eagle (2006, p. 217)

Figure 2 Pittosporum cornifolium flowers showingreproductive structures. A, Young female flowershowing large ovary and reduced stamen. B, Youngmale flower showing large stamen and reducedovary.

Figure 3 Pittosporum cornifolium type specimenillustrated by W.J. Hooker in 1832 in Curtis’sBotanical Magazine, volume 59 (pl. 3161).

Biological Flora of NZ: Pittosporum cornifolium 187

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and Jones (cover of New Zealand BotanicalSociety Newsletter 96, 2009).

Anatomy

The stem and root anatomies of P. cornifoliumappear typical of xerophytic dicotyledons.Both have thick peridermal layers, comprisingphellogen (cork cambium), phelloderm (sec-ondary cortex) and phellem (cork) (F.M.Clarkson 2011). A ring of lysigenous secretoryducts is present in the stem between theprimary phloem and cortex tissue layers(F.M. Clarkson 2011).

The leaf anatomy of P. cornifolium haspreviously been described from transverse sec-tions by Oliver (1930) and Wilkinson (1992)and more recently by F.M. Clarkson (2011).Leaf tissue layers adjacent to the leaf midribcomprise an upper cuticle, upper epidermis, athick ‘aqueous layer’/hypodermis, a closelypacked mesophyll layer composed of palisadeand spongy tissue, lower epidermis and lowercuticle. Pittosporum cornifolium leaf anatomy isconsistent with a xeromorphic form, particu-larly due to the presence of hypodermal leaftissue layers, because this layer may function asboth a water-storing tissue and a supportingtissue when cell walls become considerablythickened (Fahn 1982; Cutler et al. 2008). Inaddition, schizogenous secretory ducts havebeen noted in the midrib and scattered vascularbundles throughout the leaf (Wilkinson 1992;F.M. Clarkson 2011).

Comparative leaf anatomy of the PoorKnights Islands form and the mainland formrevealed a trend towards thicker leaf blades andleaf tissue layers in the Poor Knights Islandsform (F.M. Clarkson 2011).

Cytology

The chromosome number of P. cornifolium is2n�24 (de Lange et al. 2004). Chromosomecounts of 2n�24 have also been reported in allmembers of New Zealand Pittosporum (deLange et al. 2004).

Taxonomy and relationships

Pittosporum

Pittosporum Banks ex Gaertn, the type genus ofPittosporaceae, is represented in New Zealandand Australia and more widely throughout thePacific (as far east as the Hawaiian Islands),extending west to eastern Africa and north intoAsia (Haas 1977; Cayzer 1997). The genus nameis derived from the Greek words ‘pitta’ meaningresin and ‘spora’ meaning seed (Gaertner 1788),referring to the characteristic resinous seeds ofmost species within the genus. Pittosporumcomprises over 100 species of evergreen shrubsor trees (up to 30 m high) (Cooper 1956).

Early classification systems withinPittosporum were based on morphologicalcharacteristics such as leaf size and shape,number of valves per capsule, inflorescencetype, placenta size (Cooper 1956) and variousanatomical features such as leaf tissue layers(Wilkinson 1992). Relationships between spe-cies were postulated based on capsule valvenumber � and grouped within either bivalvedor trivalved groups (Gowda 1951). However,morphological studies within the genus havebeen complicated by the abundance of pheno-typic plasticity (ecophenetic or heteroblastic)(Chandler et al. 2007), and both hybridism andintrogression, which skew well-defined discri-minating characteristics (Allan 1961). Hencespecies delimitations and interspecific relation-ships remain unresolved for some taxa.

Although Pittosporum is abundant in Aus-tralia (Gowda 1951), the highest levels ofendemism occur in New Caledonia (45 species;Tirel & Veillon 2002), New Zealand (21 species;de Lange et al. 2010) and the Hawaiian Islands(11 species; Wagner et al. 1999).

New Zealand Pittosporum

All of the 21 New Zealand species ofPittosporum are endemic (de Lange et al.2010). Nine of these are endemic to the NorthIsland, and two to the South Island (Eagle 1982,2006). There are two further entities that require


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resolution: P. aff. crassifolium from Raoul

Island (see Eagle 2006) and the Pittosporumfound on Stephens Island, which is intermediatein appearance between P. crassifolium andP. tenuifolium. Historic relationships amongNew Zealand Pittosporum were inferred usingflower position and inflorescence type (Kirk

1899; Cheeseman 1925) and development (het-eroblastic vs. monoblastic; Allan 1961). How-ever, recent molecular data do not support thisgrouping (Hathaway 2001; Chandler et al.2007). Phylogenetic relationships among the

genera of Pittosporaceae, including New Zeal-and Pittosporum, have been assessed using theinternal transcribed spacer (ITS) region ofnuclear ribosomal DNA (nrDNA), supportingan Australian origin of the family, with all othercolonization events from Australia or from

subsequent island hopping (Chandler et al.2007). New Zealand taxa formed two distinctclades; one clade included P. cornifolium,P. pimeleoides subsp. pimeleoides andP. pimeleoides subsp. majus with affinities toNew Caledonian taxa, and the second clade

comprised all other taxa with Australian affi-nities.

Both of the proposed New Zealand radia-tions appear to be relatively recent events dueto the limited level of ITS sequence divergence.An average of 1.4% sequence divergencebetween species in the main radiation make it

an estimated 22 million years old. Theseestimates are consistent with the arrival ofPittosporum in the fossil record (Hathaway2001). The clade containing P. cornifolium andP. pimeleoides was unexpected as these specieshave not previously been grouped based on

morphology. However, this clade groupingwas consistent due to identical sequences andan average of 8.3% (47.3 bases) sequencedivergence from all other New Zealand taxa(Hathaway 2001). Hathaway (2001) proposedthat P. cornifolium and both P. pimeleoides

subspecies are the result of a more recentcolonization into New Zealand from NewCaledonia, due to their close affinities with

P. gatopenese and three other New Caledonian

taxa. Some four interspecific wild hybrids are

known within the New Zealand Pittosporum

(Druce 1977; Ecroyd 1994; B.D. Clarkson &

Clarkson 1994), but no hybrid involving

P. cornifolium has been recorded and, in

particular, no hybrid with P. pimeleoides.

Nomenclature

Pittosporum cornifolium A. Cunn. ex Hook.

was described and illustrated (pl. 3161) by W.J.

Hooker in 1832 in Curtis’s Botanical Maga-

zine, volume 59 (Fig. 3). According to Cooper

(1956, p. 163),

the species was described by W. J. Hooker frommaterial grown at the Royal Botanical Gardens,Kew, and from Allan Cunningham’s specimensand notes made by him in New Zealand in 1826.Two ‘type’ sheets in the herbarium of the RoyalBotanic Gardens, Kew, bear five labels, two sterilespecimens, a fruiting specimen and fragments offlowers. One label is dated 1826, one 1833, two1838, and one is undated. As the species wasdescribed in 1832 only part of the material canhave been available to W. J. Hooker.

Allan (1961, p. 316) gives the type locality

as ‘in humid woods on the banks of the

Kanakana [Kawakawa] and other rivers, Bay

of Islands, &c.’ and the type specimen as

‘British Museum, A. Cunningham, 1826’. The

specific epithet cornifolium refers to leaves

resembling the cornel or dogwood tree belong-

ing to the genus Cornus (Hooker 1832).Common English names used are cornel-

leaved pittosporum (Hooker 1832; Cooper

1956; Laing & Blackwell 1957), perching

pittosporum (Beever 1991) and straggling

pittosporum (Andersen 1926). Common Maori

names used are tawhiri karo, karo and whare-

whareatua (Beever 1991). Both perching ko-

huhu and perching kohukohu are common

combined English�Maori names that have

been applied (Cockayne 1967; Landcare Re-

search 2010).


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Intraspecific variation

Pittosporum cornifolium demonstrates signifi-

cant morphological and anatomical variability,

as well as genetic variation across widely dis-

tributed populations, but especially with respect

to differences between themainland populationsand Poor Knights Islands individuals.

Capsule valve numbers within this species

are inconsistent, with capsules typically being

two-valved, but occasionally producing three

(Petrie 1921; Allan 1961). Terminal umbels

vary in flower number from 2 to 10 flowers,

and occasionally to single terminal flowers(Petrie 1921; Cooper 1956). Petrie (1921) notes

that functionally male plants have higher

numbers of flowers per inflorescence than

functionally female plants. Flower colour is

variable, with reddish brown (Hooker 1982),

light red (Allan 1961) and yellow forms (Coop-

er 1956) having been recorded. From ourobservations, fully yellow forms appear to be

confined to the Poor Knights Islands plants

while pinks, reds and partial yellow coloura-

tions occur on mainland New Zealand and

other offshore islands (Fig. 1). Glasshouse

collections (2009�2010) showed that mainlandplants sourced from the Central North Island

flowered earlier (early July to late September)

than plants from the Poor Knights Islands (mid

August to late October) (F.M. Clarkson 2011).

The Poor Knights Islands form is also more

susceptible to frost, and unlike the mainland

form it does not cease growth in winter months(Smith 2004).

Continuous variation of mean leaf length

and width measures were observed from smal-

ler mainland leaf forms (across nine North

Island locations and one South Island location)

(34.5�62.6 mm and 12.4�27.1 mm, respectively)

to the larger Poor Knights Islands leaf forms(53.7�70.8 mm 27.1�36.7 mm, respectively)

(F.M. Clarkson 2011). The Poor Knights

Islands individuals are mainly distinguished

by their greater mean width. Furthermore,

maximum leaf length and width measurements

were significantly lower for mainland indivi-

duals (76 and 35 mm) when compared withPoor Knights Islands individuals (104 and50 mm, respectively) (F.M. Clarkson 2011).

Mean leaf blade thickness measures weresignificantly greater in the Poor Knights Islandsindividuals when compared with mainlandindividuals sourced from two North Islandpopulations (720 and 501 mm, respectively).

Population genetic analyses were conductedon five North Island populations (Fig. 4) andeight propagated individuals sourced from thePoor Knights Islands using inter-simple se-quence repeats (ISSRs) (F.M. Clarkson 2011).Results indicated that genetic diversity wasextremely high overall at the species level(90% polymorphic loci) but much lower at thepopulation-level (16.8%�60.9% polymorphicloci). The outcrossing dioecious breeding sys-tem of P. cornifolium is likely to be one of themost important factors influencing the observedhigh species-level diversity (F.M. Clarkson2011). Lower population-level genetic diversity(relative to intra-specific genetic diversity) islikely to result from geographic isolation. Onthe mainland, population isolation is due to theclearance and fragmentation of lowland ecosys-tems that host P. cornifolium, whereas the PoorKnights Islands are isolated from the mainlandby ocean. Overall, the Poor Knights Islandsplants exhibited the lowest levels of geneticdiversity compared with mainland populationsand were by far the most genetically distinctpopulation (F.M. Clarkson 2011).

Mantel test results revealed a significantcorrelation between genetic and geographicdistance (r�0.647, p�0.004). This furthersupports the main hypothesis that geographicisolation is the main contributing factor topopulation-level differentiation inP. cornifoliumpopulations (F.M. Clarkson 2011).

Comparisons of ITS sequence data for bothmainland and Poor Knights IslandsP. cornifolium individuals revealed a single pointmutation at 583 base pairs (F.M. Clarkson2011). This was an unexpected result, especiallyconsidering that identical ITS sequences wereobserved between mainland P. cornifolium and


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Figure 4 Observed distribution (recorded individuals; n�221) of Pittosporum cornifolium including the fiveNorth Island population sites researched by F.M. Clarkson (2011), and predicted environmental distributionbased on environmental variables (total annual rainfall, mean October vapour pressure deficits at 0900 h,mean annual temperature, mean minimum daily temperature of the coldest month, elevation, mean annualsolar radiation and mean minimum daily solar radiation in June).


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both P. pimeleoides subspecies. It is hypothe-

sized that sequence divergence in this offshore

island variant would have amaximumage that is

consistent with the isolation of the offshore

island group from the mainland (F.M. Clarkson

2011), that is, less than one million years

(Hayward 1986).Together these data on leaf anatomy, mor-

phology, population genetic structure and ITS

sequence divergence of the Poor Knights

Islands individuals may warrant the delineation

of a new subspecies, or even species (F.M.

Clarkson 2011).

Chemistry

Early phytochemichal investigation revealed

saponin and tannin in the leaves of the New

Zealand species P. cornifolium, P. crassifolium,

P. eugenioides and P. huttonianum (Greshoff

1909). Jay (1969) observed flavonoids such as

quercertin and kampferol throughout members

of Pittosporum including the New Zealand taxa

P. crassifolium, P. eugenioides, P. dallii and P.

tenuifolium. In addition, he found the flavonoid

isorhamnetin in P. eugenioides and the flavone

apigenin in P. tenuifolium. Phytosterols have

been isolated from the bark of P. colensoi and P.

eugenioides (Cambie & Parnell 1969) and poly-

acetylenes from the root of P. crassifolium

(Bohlmann & Zdero 1975 as cited in Nemethy& Calvin 1982).

Reproductive biology

Flowering

Pittosporum cornifolium flowers annually andhas an autumn�spring flowering season extend-ing from May to October with peak floweringin September (Fig. 5) (F.M. Clarkson 2011).Petrie (1921) noted the tendency for maleplants to produce more flowers than femaleplants, with male plants producing terminalumbels with up to 10 flowers (usually six toeight), and female plants producing singleterminal flowers.

Pollination and seeding

Individual plants are typically dioecious (Petrie1921). However, plants grown from cuttings offan apparently dioecious male plant have pro-duced infrequent capsules (F.M. Clarkson2011). Godley (1979) has described this ‘incon-stant male’ trait among other dioecious generain New Zealand. Thus, P. cornifolium appearsto be subdioecious, outcrossing is likely to bethe preferential mode of fertilization but self-fertilization may also be possible (controlledstudies have yet to be undertaken to confirmthis) (F.M. Clarkson 2011). Capsules can be

Figure 5 Phenology calendar for Pittosporum cornifolium based on North Island field survey, AK, WAIK,NZFRI and CHR herbarium data, NVS and LENZ data banks and unpublished observations (n�105).


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found on female plants all year round and oftengreen capsules are present from the currentflowering year together with dehisced capsulesfrom the previous year (Fig. 5).

Although no records of specific insectpollinators exist, P. cornifolium is thought tobe entomophilous due to its small flower sizeand the absence of features adapted to pollina-tion by birds (Webb et al. 1999). Thesecharacteristics are consistent throughout NewZealand Pittosporum taxa (Webb et al. 1999).Insect visitations have been recorded forP. tenuifolium by beetle species, Erirhinuslimbatus and Tigones caudata (Thomson1926), and numerous Diptera (fly) species(Heine 1937); for P. crassifolium by fly species,Calliphora stygia and Syrphus novae-zelandiae,members of families Tachinidae and Opomyzi-dae, the introduced bee Apis mellifera (Heine1937) and insect orders Coleoptera, Hymenop-tera and Hemiptera (Anderson 2003); and forP. eugenioides by introduced flies (Thomson1926).

However, Anderson (2003) has also re-corded bird visitations to P. crassifolium bythe endemic honey eaters, tui (Prosthemaderanovaeseelandiae) and bellbird (Anthornismelanura); this association was previouslyunderestimated and suggests birds may beactive pollinators among other members ofthe New Zealand Pittosporum. Castro andRobertson (1997) document visitation ofP. cornifolium flowers by endemic honeyeatershihi (Notiomystis cincta) and bellbird; thisfurther suggests birds may have a largerinfluence in the active pollination ofPittosporum than first suspected.

After fertilization, the ovules develop intoblack seeds (see morphology). Mature capsulesopen to reveal vermilion stained interiors withseeds immersed in a sticky resin (Cooper 1956;Poole & Adams 1994). Pittosporum cornifoliumis thought to be bird dispersed due to itsresinous seeds (Oliver 1930; Burrows 1994),the vermilion red inner capsule coating mayalso act as an attractant. Oliver (1930) recordsP. cornifolium seeds being accidentally attached

to feathers which would serve as a dispersal

mode, and Powlesland (1987) has recordedconsumption of the seed by native kokako(Callaeas cinerea), however, tests to determinewhether seeds are viable once passed throughthe gut have yet to be conducted.

No information is available on seed viabi-lity and seed germination rates but results forP. obcordatum (B.D. Clarkson & Clarkson1994) show that seed from female plantsgerminated readily but seed collected frominconstant males failed to germinate.

Lifespan and population structure

No published data on lifespan have been found.One individual growing on the University ofWaikato campus in Hamilton is known fromplanting records to be at least 34 years of age.An estimated age of c. 42 years and a diametergrowth rate of 0.09 cm per year were extra-polated for the main trunk (3.9 cm) by counting12 assumed annual growth rings on a 1.1 cm

diameter side branch. This specimen is in goodhealth and actively growing, indicating thatP. cornifolium may live for 50 years or more.

In a study of five North Island populations(Fig. 4), height and width estimates and repro-ductive status of P. cornifolium individuals wereobtained to determine population (life stage)structure (Fig. 6) (F.M. Clarkson 2011). Thefive populations displayed a range of life-stagestructures. Only two of the populations exhib-ited recent regeneration (Square Kauri and The309 Road) and of the remaining three popula-

tions, only Raglan Harbour had individuals inthe juvenile size class (Fig. 6). The remainingtwo populations, Maungatautari and New Ply-mouth, were entirely composed of adult indivi-duals (Fig. 6). The combined sex ratio of thesepopulations was slightly skewed with a higherproportion of male to female individuals (61: 39respectively). However, all of the populationscontained reproductively mature female plantswhich flower regularly, producing capsules and

seed (F.M. Clarkson 2011).


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Distribution

Geographic range

The known range of P. cornifolium extendsfrom the North Cape (North Island) to the

Marlborough Sounds and Paparoa Range(South Island) with a southern limit near Barry-town on the West Coast (latitude 42815?S;Cooper 1956). It also occurs on numerousnorthern offshore islands such as TawhitiRahi/Poor Knights Islands, Taranga/Hen Is-

land, Hauturu/Little Barrier Island, Aotea/Great Barrier Island, Kawau Island and Wai-heke Island (Cooper 1956) (Fig. 4) (F.M.

Clarkson 2011).

Environmental range

Throughout its geographic range, P.

cornifolium can be found in a variety ofrupestral and forest ecosystems within anelevation range of 0�786 m above sea level

and a mean elevation of 248 m above sea level(F.M. Clarkson 2011). A predicted environ-

mental distribution map was developed fromrecorded Pittosporum cornifolium locations(n�221) which were overlain on Land Envir-

onments of New Zealand (LENZ) environmen-tal surfaces (Leathwick et al. 2003) to obtainminimum and maximum values of selected

environmental variables (Fig. 4, Table 1)

(F.M. Clarkson 2011). Pittosporum cornifoliumis distributed widely in the coastal and lowlandzones of the North Island. However, there aresome obvious gaps in both its observed andpredicted distribution (Fig. 4). Gaps in theobserved distribution that are inconsistentwith potential environmental distribution in-clude the Waikato basin where environmentalvariables are favourable but the area wasformerly dominated by extensive wetland sys-tems and thus lacks appropriate habitat (B.R.Clarkson 2002). The environment is suitablesouth of the Wairoa lowlands in the Wairarapabut there are no current records, probablybecause nearly all lowland forest in the areahas been cleared (Nicholls 1980). Similarly,much of the Taupo Volcanic Zone is favourablein terms of the predicted environmental dis-tribution of P. cornifolium, but observed ab-sences are likely to be due to the ecologicalimpact caused by the 232 AD (Hogg et al. 2011)Taupo eruption. Both Mahia in the NorthIsland and Banks Peninsula in the South Islandare also environmentally favourable locationswhere P. cornifolium has not been recorded.The often companion obligate epiphyteGriselinia lucida is present at both of theselocalities: Banks Peninsula (Laing 1919) andMahia (Whaley et al. 2001). Additionally,many predominantly North Island warm�temperate species such as nikau (Rhopalostylis

Figure 6 The population (life stage) structure of five North Island populations of Pittosporum cornifolium:The 309 Road (Coromandel), Square Kauri (Coromandel), Maungatautari (Waikato), Raglan Harbour(Waikato) and New Plymouth (Taranaki).


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sapida) are found growing in the BanksPeninsula area (Wilson 2002). Pittosporumcornifolium is largely unrecorded from the driereastern side of the North Island where nativeforests have been almost completely removed,and the low rainfalls are not conducive to richepiphyte floras (B.R. Clarkson & Clarkson1991). Absence from the Wairoa, Gisborneand Waiapu lowlands was predicted due tothe high mean October vapour pressure deficitsexceeding 0.47 kPa (F.M. Clarkson 2011).Pittosporum cornifolium was absent from theKaimanawa and Ikawhenua ranges in theCentral North Island in both observed andpredicted distribution maps. Mean daily tem-perature minimums for the coldest month arelower than 0.6 8C in the area. Pittosporumcornifolium has both restricted observed dis-tributions and predicted distributions in theSouth Island; these limits are set primarily bylow mean daily temperature minimums of thecoldest month (B 0.6 8C), but also from acombination of low mean annual temperature(B 9.6 8C), low mean annual rainfall (B 937mm), low mean annual solar radiation (B 13.1kJ/m2/day), low mean minimum solar radiationin June (B 4.2 kJ/m2/day) and high elevation(� 786 m) (Table 1) (F.M. Clarkson 2011).

Plant communities

Pittosporum cornifolium is represented in arange of lowland and coastal forest, and rupes-tral ecosystems. Within this range, it exhibitsthree distinct lifestyles; epiphytic, terrestrial and

rupestral, the most common being the epiphytic

lifestyle. The overall lifestyle statistics obtained

from herbarium records (n�92) and an ecolo-

gical survey of five North Island populations

(n�110) were 107 (53%) epiphytic, 52 (26%)

terrestrial and 43 (21%) rupestral (F.M. Clark-

son 2011). A combination of field survey data

from the North Island and herbarium data sets

(n�142) revealed P. cornifolium were recorded

in 20 different vegetation types (Table 2), all of

Table 1 Summary statistics of environmental variables from known plot locations of Pittosporum

cornifolium. Environmental variables include: total annual rainfall (r), mean October vapour pressuredeficits at 0900 hours (vpd), mean annual temperature (mat), mean minimum daily temperature of the coldestmonth (tmin), elevation, mean annual solar radiation (mas) and mean minimum daily solar radiation in June

(junes).

Rain (mm) vpd (kPa) mat (8C) tmin (8C) Elevation (m) mas (kJ/m2/day) junes (MJ/m2/day)

Mean 1841.7 0.32 13.2 5.0 247.8 14.8 5.9

Minimum 937.0 0.23 9.6 0.6 1.0 13.1 4.2Maximum 3321.0 0.47 15.7 8.7 786.0 15.5 7.1

Table 2 Vegetation types containing Pittosporumcornifolium based on North Island field survey anddata from herbarium records (n�142).

Vegetation types Count

Kauri Forest 58Rupestral Shrubland 30

Rimu/Tawa Forest 16Tawa�Broadleaved Forest 8Pohutukawa Forest 4Tıtoki�Pukatea Forest 3

Tawa�Mixed Podocarp Forest 3Puriri Forest 3Pukatea�Tawa Forest 3

Hard Beech Forest 2Mataı�Tıtoki Forest 2Kanuka�Manuka Scrub 2

Swamp Maire Forest 1Alder�Willow Forest 1Mangeao�Tawa Forest 1

Hınau/Kanuka Forest 1Northern Rata/Tawa Forest 1Kamahi�Ixerba Forest 1Tawa�Taraire Forest 1

Broadleaved�Conifer Forest 1


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which were forest except for rupestral shrubland(F.M. Clarkson 2011). The three most commontypes included kauri (Agathis australis) forest,rupestral shrubland and rimu/tawa (Dacrydiumcupressinum/Beilschmiedia tawa) forest.Although it is never a dominant component ofthese types, P. cornifolium occasionally attainsco-dominant status in the rupestral commu-nities of Raglan Harbour.

Lowland and coastal forest communities

Pittosporum cornifolium occurs in several NewZealand lowland forest types including kauri,mixed podocarp, coastal pohutukawa(Metrosideros excelsa) and broadleaved foresttypes. Within these lowland forest systems,where it exhibits both epiphytic and terrestriallifestyles, the species appears to have an affinityto older growth forest and/or remnant oldgrowth trees (F.M. Clarkson 2011).

The tall kauri forests of the North Island,which usually occur on well-drained hill sides(Oliver 1930), host P. cornifolium of bothterrestrial and epiphytic lifestyles. Within thisforest type, P. cornifolium has been foundgrowing abundantly in the crowns and directlybeneath the crowns of large old growth kauritrees, on the trunks of tree fern species Cyatheadealbata and C. cunninghamii, and in associa-tion with Collospermum hastatum, Asteliasolandri, A. trinervia and Brachyglottis kirkii(F.M. Clarkson 2011).

Podocarp-dominant lowland forests, withtheir dense canopy of foliage, contain the great-est diversity of epiphytes (Oliver 1930). Withinthese forests, P. cornifolium can be found on avariety of host trees including: rimu (Dacrydiumcupressinum), totara (Podocarpus totara), mataı(Prumnopitys taxifolia) and kahikatea(Dacrycarpus dacrydioides) and grow primarilyin association with C. hastatum and A. solandri(F.M. Clarkson 2011).

Broadleaved dominant lowland forests alsoprovide a range of canopy hosts. These includetawa (Beilschmiedia tawa), taraire (Beilschmiediataraire), pukatea (Laurelia novae-zelandiae),

puriri (Vitex lucens) and tıtoki (Alectryonexcelsus), and again P. cornifolium grows pri-marily in association with C. hastatum and A.solandri (F.M. Clarkson 2011).

The main coastal forest hosts are po-hutukawa (Metrosideros excelsa) and puriri(F.M. Clarkson 2011). Kirk (1872) noted abun-dant epiphytic Griselinia lucida, P. cornifoliumand A. solandri on Tarawera lake shore po-hutukawa prior to the 1886 eruption. Largepuriri growing around the Raglan Harbour,Waikato, also host epiphytic P. cornifolium(F.M. Clarkson 2011).

Other associated species in lowland andcoastal forests include Metrosideros fulgens,Asplenium polyodon and Microsorumpustulatum (F.M. Clarkson 2011).

Rupestral communities

Pittosporum cornifolium can be found growingas a rupestral in coastal rock communitiesincluding Maunganui Bluff (G. Bowden, Ta-wapou Nursery, pers. comm. 2010), WaihekeIsland, Poor Knights Islands (Cooper 1956),and Raglan Harbour where P. cornifoliumgrows as a co-dominant species amongst scrubcommunities of A. banksii and Griselinia lucida(F.M. Clarkson 2011).

Succession

Oliver (1930) describes the general pattern ofepiphyte succession in New Zealand forests asfollows: primary colonization of bark by smalllichens and mosses, which facilitate (by sub-strate alteration) the establishment of ferns ororchid species. The increase in communitycomposition encourages further establishment(i.e. lichens and mosses adhere to fern rhizomesor aerial roots of orchids), while exfoliated barkand fallen leaves are caught and decay toproduce a fine, low nutrient, gritless soil thatcollects in large quantities (vertical branchesmay support soil layers as thick as a third of thebranch diameter). Moisture is retrieved directlyvia rainfall or indirectly via trunk runoff, while


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evaporation is retarded by the covering offoliose lichens (Oliver 1930).

Epiphytic P. cornifolium is late successionalas it commonly colonizes already establishednest hosts A. solandri and Collospermumhastatum (Oliver 1930; B.D. Clarkson 1985;Burns & Dawson 2005; F.M. Clarkson 2011).Nest epiphytes facilitate the establishment oflarger shrub epiphytes like P. cornifolium byproviding a source of organic matter andmoisture, thereby enhancing microclimate suit-ability (see Dickinson et al. 1993).

Rupestral individuals at Raglan Harbourwere also found growing in association withnest host species (A. banksii), where facilitationby the nest host is likely, as P. cornifoliumindividuals were notably absent from raw rocksurfaces (F.M. Clarkson 2011).

The detritus substrate of terrestrial indivi-duals growing beneath kauri stands in theCoromandel Peninsula is composed of mostlybrown loam soils, which are typically lownutrient and acidic (Molloy 1998). Detritussubstrates are a result of long-term soil develop-ment by gradual erosion and the build up oforganic matter provided by old growth kauriforest systems. Therefore, the build up ofdetritus soils in old growth systemsmay facilitatethe establishment of terrestrial P. cornifolium asdoes substrate development in canopy andrupestral systems (F.M. Clarkson 2011).

Conservation and restoration

Conservation status

The loss of lowland and coastal habitat in theWaikato region (Leathwick et al. 1995), and inthe majority of ecological regions around NewZealand (McGlone 1989), has meant that thehistorical range of P. cornifolium is significantlyreduced and its populations depleted. Addi-tionally, the strong habitat specificity ofP. cornifolium restricts it to habitats of verylimited extent (F.M. Clarkson 2011).

Although P. cornifolium can be locallyuncommon, it does not currently meet thespecific criteria (see de Lange et al. 2009) to

be considered nationally threatened (F.M.Clarkson 2011). It is found in numerousprotected natural areas including nationalparks, scenic reserves and QE II open spacecovenants. However, there is no doubt that itsrange has been reduced and that it has been lostfrom a number of sites where it was previouslycollected (F.M. Clarkson 2011). Observationsalso suggest that it is palatable to possums, andpossum browsing may have contributed to thereduction of some populations (Ravine 1995;Mitcalfe & Horne 2005). Its epiphytic cogener,P. kirkii is classified as declining (de Lange etal. 2009). Surveillance of P. cornifolium popula-tions may be warranted to detect gradual orsudden decline.

Restoration

To date, only a few restoration projects aroundNew Zealand appear to have considered thereintroduction of P. cornifolium. These includeKarori Sanctuary (Karori Sanctuary Trust2008), Matakohe Island (Ritchie 2000) andMotuihe Island (Hawley 2005).

Conservation efforts should be focused onretaining substantial populations in large re-serves while restoration is required wherenumbers are reduced or the species has beenrecently lost.

The significant correlation between geo-graphic distance and genetic differentiationamong five North Island populations ofP. cornifolium highlights the importance ofplant provenance and associated ecotypeswhen sourcing seed for restoration (F.M.Clarkson 2011). The concept of ecologicalmicrohabitats is also important, especially inconsideration of the different lifestyles ofP. cornifolium in a range of lowland and coastalecosystems (epiphytic, rupestral and terres-trial). Ideally, source sites would be both theclosest to the restored site (to maintain prove-nance) and be a similar ecosystem to the one inneed of restoring (F.M. Clarkson 2011).Furthermore, seeds should be collected fromas many individuals as possible to maintain


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levels of genetic diversity similar to that ofsource populations (F.M. Clarkson 2011).

Conclusion

Pittosporum cornifolium has been described byOliver (1930) as a typical epiphyte in that thespecies is habitually epiphytic. However,although it is more commonly epiphytic, it canalso be found growing in abundance in terres-trial and rupestral lifestyles. With this diversityof lifestyles, P. cornifolium may be considered afacultative epiphyte as defined by Benzing(2004). Using the lifestyle statistics presented(see Plant Communities), the null model forBenzing’s classifications developed by Burns(2010) places P. cornifolium as a facultativeepiphyte. Epiphytes become increasingly facul-tative as environmental conditions in tree ca-nopies converge on terrestrial environmentalconditions (Benzing 2004). The strong habitatspecificity of P. cornifolium restricts it to low-land and coastal habitats of very limited extent,which are widely yet discontinuously distribu-ted. Environmental factors that may restrictdistribution include high vapour pressure defi-cits, cooler temperatures, limited rainfall, lim-ited solar radiation and higher elevations.Edaphic range is characterized by low nutrientsubstrate types. The distinctive leaf morphologyand anatomy, as well as the differentiatedpopulation genetic structure and ITS sequencedivergence, in the Poor Knights Islands indivi-duals suggest that recognition of a new taxonmay be warranted. This requires detailed ex-amination of the taxon across its mainlandrange, the Poor Knights Islands, and othernorthern offshore islands where the species ispresent. Although P. cornifolium can be locallyuncommon across its known range, it does notcurrently meet the specific criteria to be con-sidered regionally or nationally threatened.However, there is no doubt that its range hasbeen reduced and that it has been lost from anumber of sites where it was previously col-lected. Key considerations for the conservationand restoration of this species in areas in which

populations have been depleted or completelydisplaced include sourcing for local provenanceand specific microhabitats and associated life-styles. Finally, future research should focus onbaseline ecological research including decipher-ing pollination and dispersal modes, as well asgermination and seed viability trials, as this isfundamental to developing informed conserva-tion and restoration strategies.

Acknowledgements

We gratefully acknowledge access provided by Land-

care Research to the National Vegetation Survey

Databank (NVS) and Land Environments of New

Zealand (LENZ). We thank the following herbaria

for access to their records, University of Waikato

(WAIK), Allan (CHR), Auckland Museum (AK),

Museum of New Zealand Te Papa Tongarewa

(WELT) and New Zealand Forest Research Institute

(NZFRI). This project was aided by funding grate-

fully received from the University of Waikato

Masters Scholarship and the George Mason Chari-

table Trust. We also appreciate comments and

contributions from Dr Bev Clarkson, Dr Jake Over-

ton, Toni Cornes and Catherine Bryan.

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biological flora of new zealand 13. pittosporum cornifolium , tāwhiri...

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