morphological and anatomical development in the vitaceae. vii. floral development in ...

Morphological and anatomical development in theVitaceae. VII. Floral development in Rhoicissusdigitata with respect to other genera in the family

Jean M. Gerrath, T. Wilson, and Usher Posluszny

Abstract: This study forms part of our series of investigations on genera in the Vitaceae and is the first developmentalstudy for the genus Rhoicissus. Vegetative and reproductive development of shoot apices of Rhoicissus digitata (L.f.)Gilg et Brandt were examined using epi-illumination light microscopy and scanning electron microscopy. Leaf-opposedtendrils or inflorescences, typical of the shoot architecture in the Vitaceae, were present at every node. Macro-scopically, the shoot appears to grow either monopodially or sympodially. At the microscopic level, however, shootdevelopment is sympodial; the shoot apical meristem bifurcates unequally, with the larger portion forming an uncom-mitted primordium, which will become either an inflorescence or a tendril, and the smaller portion (in the position ofthe axillary bud) forming the new shoot apical meristem. Floral primordia first initiate three sepals followed by a calyxring on which the last two sepal primordia form. The five petals are initiated in a whorl followed by the five stamensin a petal-opposed position. There is no evidence of a common petal–stamen primordium in this species. The gy-noecium is initiated as a ring primordium. Subsequently, the four ovules are initiated at the base of the two septa thatgrow out from the inner gynoecial wall. The nectary disc forms as an outgrowth of the gynoecium base. Mature flow-ers have greenish petals and a red nectariferous disc. Flowers are bisexual, and seed germination is approximately 63%.Unlike previous studies in Vitis and Parthenocissus, Rhoicissus appears to have few putatively derived floral develop-mental characters, which would support its relatively basal position in current phylogenies for the family.

Key words: Vitaceae, morphology, development, shoot architecture, flower.

Résumé : Les auteurs présentent une nouvelle étude dans leur série de travaux sur les Vitaceae; il s’agit de la premièreétude développementale pour le genre Rhoicissus. À l’aide de l’épi-illumination en microscopie optique et du balayageen microscopie électronique, ils ont examiné le développement végétatif et reproductif des apex caulinaires du Rhoicis-sus digitata (L.f.) Gilg et Brandt. Des vrilles opposées à des feuilles ou à des inflorescences, ce qui est typique del’architecture des tiges chez les Vitaceae, se retrouvent à tous les nœuds. Macroscopiquement, la tige semble croîtremonopodialement ou sympodialement. Au niveau microscopique, cependant, le développement de la tige est sympodial;le méristème apical de la tige bifurque de façon inégale, la portion la plus grosse formant un primordium indéterminé,qui deviendra soit une inflorescence ou soit une vrille, et la portion plus petite (dans la position du bourgeon axillaire)formant le nouveau méristème apical de la tige. Les primordiums floraux générent au départ trois sépales, suivis d’unanneau du calice sur lequel se forment les primordiums des deux derniers sépales. Les cinq pétales s’initient dans unverticille, suivis par les cinq étamines dans une position opposée aux pétales. Il n’y a pas de preuve qu’un primordiumcommun aux pétales et aux étamines existe chez cette espèce. Le gynécée est initié sous forme d’un primordium annu-laire. Subséquemment les quatre ovules débutent leur formation à la base de deux septums qui se développent à partirde la partie interne de la paroi gynéciale. Le disque des nectaires apparaît comme une excroissance à la base du gy-nécée. Les fleurs matures ont des pétales verdâtres et un disque nectarifère rouge. Les fleurs sont bisexuées, et la ger-mination des graines d’environ 63 %. Contrairement aux études antécédentes, chez les Vitis et Parthenocissus, lesRhoicissus semblent avoir peu de caractères putativement dérivés du développement floral, ce qui supporterait sa posi-tion relativement basale dans les phylogénies courantes de la famille.

Mots clés : Vitaceae, morphologie, développement, architecture de la tige, fleur.

[Traduit par la Rédaction] Gerrath et al. 206

Introduction

The grape family (Vitaceae) is a relatively small family ofabout 14 genera and 700 species (Süssenguth 1953). It con-

tains the commercially important species Vitis vinifera, thewine grape, about which much is known. However, surpris-ingly little is known about the rest of the family, especiallyfrom a botanical perspective. This might be partly because

Can. J. Bot. 82: 198–206 (2004) doi: 10.1139/B03-120 © 2004 NRC Canada

198

Received 6 June 2003. Published on the NRC Research Press Web site at http://canjbot.nrc.ca on 5 March 2004.

J.M. Gerrath.1 Department of Biology, University of Northern Iowa, Cedar Falls, IA 50614-0421, U.S.A.T. Wilson and U. Posluszny. Department of Botany, University of Guelph, Guelph, ON N1G 2W1, Canada.

1Corresponding author (e-mail: [email protected]).

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most species are tropical or subtropical Southern Hemi-sphere lianas, found in regions of the world that are under-represented by botanists. In addition, although the genera aredistinguished from one another largely on the basis of floralcharacters (Süssenguth 1953), flowers are generally small,inconspicuous, and ephemeral, making the Vitaceae a diffi-cult family to study.

The genus Rhoicissus Planch., native to eastern Africa(from Arab regions in the northeast as far south as SouthAfrica), contains about 12 species. Süssenguth (1953) de-scribed it as a climbing shrub whose tendrils lack adhesivediscs, with flowers usually in fairly crowded, tendril-less,short pedunculate cymes. Urton et al. (1986), however,stated that inflorescences of Rhoicissus tridentata may beassociated with tendrils. The genus has apparently bisexualflowers, five to seven firm-fleshed petals that are recurved atanthesis, a relatively short, cylindrical style, and a ring-shaped disc that is attached to the ovary, forming a basalring on the mature fruit. As best as we can determine, botan-ical descriptions of this genus are from herbarium specimensor limited observations of plants in the wild. Thus, this paperis the first report of the floral development and biology ofthe genus based on long-term observations of living mate-rial.

The lack of information on Rhoicissus is not unusual inthe family, and this has contributed to a paucity of hypothe-ses of phylogeny of the genera within the family. The mostcomplete and current phylogenetic hypothesis concludedthat along with Ampelopsis, Clematicissus, Cissus, and Am-pelocissus, Rhoicissus forms a series of successively branch-ing sister clades to other Vitaceae (Ingrouille et al. 2002). Ofthese genera, Rhoicissus appears to be most closely allied toAmpelopsis, based mainly on rbcL data (Ingrouille et al.2002). The information presented in their paper allowed usto test this hypothesis from a developmental morphologicalperspective using previously published studies on vegetativeand floral development in other species in the family.

Using seed-grown plants of Rhoicissus digitata (L.f.) Gilget Brandt and their offspring, we were able to examine bothvegetative shoots and floral development. Specifically, theobjectives of this study were to (i) document the ontogeny ofboth vegetative and floral organs in this species, (ii) compareour results with what is known about these characters inother genera in the family, and (iii) relate our results to cur-rent phylogenetic hypotheses for the family.

Materials and methods

Rhoicissus digitata is usually found in riparian fringingvegetation and is reported from Natal, Transvaal (SouthAfrica), and Mozambique (Wild and Drummond 1966).Although R. digitata has shown promise as a horticulturalfoliage plant that roots well from cuttings (Kæmpe et al.1989), it is not commercially common.

Seeds of R. digitata were obtained from Chiltern Seeds(Bortree Stile, Ulverston, Cumbria LA12 7PB, England),sown in Redi Earth® seed starter soil, and transplanted indi-vidually after the seedlings had reached sufficient size.Plants were then integrated into the teaching displays of boththe University of Guelph Bovey greenhouse and the Univer-sity of Northern Iowa Biology Botanical Center and were

watered, fertilized with liquid 20–20–20 fertilizer biweekly,and repotted as needed. All flowering material was obtainedfrom two plants growing at the University of Northern IowaBiology Botanical Center. Twenty fruits were collected fromone plant in January 2001 and dried for 6 weeks. The seedswere then removed from the fruits and planted in RediEarth® seed starter soil. Fifteen fruits were left to dry on thevine and then picked and planted directly into the same typeof soil. Germination occurred over a period of 4–8 weeks.

Dissecting microscopyLiving shoots and flowers were examined under an Olym-

pus SZ60 dissecting microscope and photographed withFujicolor 200 film using an Olympus PM20 automatic cam-era.

Epi-illumination light microscopyVegetative shoot apices and developing flowers were har-

vested and placed in formalin – acetic acid – alcohol (10%formalin – glacial acetic acid – 95% ethanol – deionized wa-ter (1:1:9:9)). Material was then dissected, carried throughan ethanol dehydration series, and stained in 0.1% nigrosinin 95% ethanol at least overnight until the material wasdeemed sufficiently stained. Observations were made with aZeiss photomicroscope III (Carl Zeiss Inc., Toronto, Ont.),fitted for epi-illumination light microscopy (Posluszny et al.1980; Charlton et al. 1989), and captured using NorthernEclipse software. Images were assembled using Adobe®

Photoshop® 6.

Scanning electron microscopySamples were fixed in formalin – acetic acid – alcohol

and dehydrated in 100% ethanol in the same manner as de-scribed for epi-illumination light microscopy and then criti-cal-point dried using a LADD critical point drier (LADDResearch Industries, Burlington, Vt.). Dried samples wereadhered to metal stubs using double-sided tape and thenwere coated with a 30-nm gold–palladium layer in an Emi-tech K-550X sputter coater (Emitech, Ashford, Kent, Eng-land). Samples were observed at 8 kV using a Hitachi S-570scanning electron microscope (Hitachi, Tokyo, Japan). Im-ages were acquired using version 5.1 Quartz PCI (QuartzImaging Corp., Vancouver, B.C.) with an image resolutionset at 1696 × 2048 pixels.

Results

Shoot organography and architectureUnder greenhouse conditions, this species is a vine,

climbing by leaf-opposed tendrils (Fig. 1a). Leaves are com-pound, usually trifoliolate, although palmately compoundleaves with four or five leaflets are not rare. Tendrils andaxillary buds are present at every node (continuous), whichconforms to architectural pattern 5 for this family (Gerrathet al. 2001). Tendril production is facultative, and occasion-ally an extremely vigorous shoot will fail to produce tendrilsfor many nodes, although they will be present on axillarybranches on this shoot. Tendrils are unbranched, althoughbracts containing rudimentary buds are present on the aba-xial face of each tendril (Fig. 1a, arrowheads). On the shoot,

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axillary buds may remain dormant or may grow out to reiter-ate the main shoot pattern.

Inflorescences are leaf opposed, in the same position as

tendrils (Figs. 1b and 1c). Once an inflorescence develops, itmay dominate the growth of the main shoot, giving the ap-pearance of a sympodial pattern of growth (Fig. 1b), or the

Fig. 1. Vegetative and reproductive shoot architecture. (a) Habit photograph of vegetative shoots showing an unbranched tendril (T) op-posite a leaf at every node (continuous). Axillary buds or branches are also continuous at every node. Arrowheads indicate bracts ontendrils. SAM, shoot apical meristem; L, leaf. Actual size. (b) Dissecting photomicrograph showing a reproductive shoot complex inwhich the leaf-opposed inflorescence (I) dominates the much smaller main shoot (SAM). (c) Photograph using a dissecting microscopeshowing a reproductive shoot in which the leaf-opposed inflorescence is much smaller than the main shoot (SAM) and appears clearlylateral.



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Fig. 2. Developmental stages of apical meristems, inflorescence primordia, and flowers. (a) A leaf primordium (L) with stipules (S)has initiated on the periphery of the shoot apical meristem (SAM). Similarly, a bract (b) has initiated on the periphery of the main arm(MA). UP, uncommitted primordium. (b) An uncommitted primordium has initiated high on the periphery, opposite a leaf (L), and as amuch larger portion than the shoot apical meristem. Also, an uncommitted primordium has unevenly bifurcated into a larger main armand a smaller lateral arm (LA). (c) Three sepal primordia (K) arise on the flank of a flower primordium (F). (d) Individual sepals arenot discernible on the ring-like calyx (K). (e) Simultaneously, five petal primordia (P) arise low on the periphery of the floral apex (F).( f ) Petal primordia begin to grow up and become pointed knobs around a distinctly flat floral apex. (g) Stamen primordia (A) simulta-neously arise in a petal-opposed position, internal to the petals. Each petal primordium grows inward to curve over a stamen andenclose the floral apex. (h) Stamens grow into rounded isodiametric knobs. (i) Stamens become flattened and a gynoecial ring primor-dium (G) arises from the floral apex. (j) The gynoecial ring primordium grows upward as the stamens begin to form bithecal struc-tures. (k). As the gynoecium continues its upward growth, a basal disc (D) begins to form as protrusions between the stamens. (l) Thebasal disc has developed into a flat structure surrounding the stigma and style (Si). (m) Four ovules (O) have formed in the ovary sur-rounded by the gynoecial disc. Two extensions of the ovary wall appress each other to form a septum (Se). (n) Ovules are anatropousand bitegmic. Figures 2a, 2d, 2g, 2h, 2i, 2l, and 2n: scanning electron microscopy; scale bars = 100 µm; Figs. 2b, 2e, 2f, 2j, and 2k:epi-illumination microscopy; scale bars = 100 µm; Figs. 2c and 2m: scanning electron microscopy; scale bars = 500 µm.



main shoot may continue its dominance relative to the inflo-rescence, giving the appearance of a monopodial branchingpattern (Fig. 1c).

As plants increased in size, they produced root tubers (notshown). Hand sections showed that these swellings along theroot had a well-developed periderm and tested positive forstarch with iodine potatassium iodide (data not shown). Theydid not produce shoot buds, even when replanted separatelyfrom the main plant. Thus, the tubers appear to function instorage rather than in vegetative propagation.

Shoot developmentLeaves, which can appear as broadly flattened primordia

(Fig. 2a), are initiated high on the flank of the shoot apicalmeristem. The leaf primordium with two stipules forms acollar that extends about two-thirds around the circumfer-ence of the shoot apex (Fig. 2a). The uncommitted pri-mordium is initiated opposite and after the leaf as the resultof unequal bifurcation of the shoot apical meristem (Figs. 2aand 2b). The larger portion will become the uncommittedprimordium, and the smaller portion, in the position axillaryto the leaf, will form the shoot apical meristem (Fig. 2b). Asit matures, the uncommitted primordium will form a bracton its abaxial face in the same axis of orientation as theleaves on the main shoot (Figs. 2a and 2b). Subsequently,the uncommitted primordium forms an unequal bifurcationin which the larger portion remains as the main arm and thesmaller portion forms the lateral arm (Fig. 2b).

Inflorescence and floral developmentThe inflorescence is cymose, with sparsely compound di-

chasia on which a small number of flowers are produced(Fig. 3). The first indication of floral development is the ini-tiation of three sepals on the flank of the floral apex(Fig. 2c). This is followed by the formation of a roughlyfive-lobed calyx ring (Fig. 2d). Floral development is notsynchronous within a dichasium, and the lateral flower pri-mordium has not initiated any sepal primordia (Fig. 2d).Petal primordia are initiated in a whorl of five (Figs. 2e and2f ). Their position relative to the sepals is assumed to be al-ternate, but clarification of this point is difficult, since bythis stage the individual sepals have been supplanted by thecalyx ring (Fig. 2d ).

The five stamen primordia are initiated opposite the pet-als, which by this stage are dorsiventrally flattened andcurved sufficiently to cover the stamen primordia (Fig. 2g).As floral development proceeds, the developing petals covereach stamen (Fig. 2h). The gynoecium is first visible as acentral depression in the floral apex (Fig. 2i). As flower de-velopment continues, the ovary wall forms a gynoecial ringat about the same time as the bifurcation of the anthers intoseparate microsporangia (Fig. 2j ).

The tissue at the base of the ovary grows out between thestamens and will eventually form the nectariferous disc(Fig. 2k). Later, the base of the ovary appears horizontallyflattened as the result of the disc development (Fig. 2l ). Tri-chomes are evident by this stage on the abaxial surface ofthe petals, as they cover the anthers, which have developedtheir four microsporangial chambers (Fig. 2l ).

The ovary is two-loculed, as the result of the inwardgrowth of septa formed on opposite sides of the ovary wall

(Fig. 2m). Each chamber contains two anatropous, bitegmicovules (Figs. 2m and 2n).

Externally, the inflorescences have few flowers. Petals arevalvate (Figs. 4a and 4b) and both they and the calyx ringhave hairs (Fig. 4a). As anthesis begins, the petals recurve,and their slightly cucullate tips become obvious (Fig. 4b).As anthesis progresses, the petals recurve fully, the filamentselongate, the capitate stigma is exposed, and nectar is se-creted from the disc (Fig. 4c). Both the petals and stamensdehisce, leaving a reddish stigma (Fig. 4d). The gynoecialbase is buried in the disc, giving the appearance of a peri-gynous ovary (Fig. 4d).

Fruit set and seed germinationWe could find no morphological differences among flow-

ers in this species. This, coupled with the fact that fruit setoccurred when only one plant flowered, leads us to concludethat flowers are both structurally and functionally hermaph-roditic. Fruits took 2–3 months to ripen to a deep blue–blackcolour (Fig. 4e). Of 20 fruits collected, 9 had 2 seeds perfruit and 11 had 3 seeds per fruit. There were no fruits witheither 1 or 4 seeds per fruit.

Forty-six seedlings from the original plants grew largeenough to assess seedling morphology. There was a hetero-blastic leaf sequence in which the first true leaf was alwayssimple, and all leaves were trifoliolate by node 4. The ma-jority (76%) produced their first trifoliolate leaf at node 3.Eighteen seedlings grew large enough to produce tendrils,with the first one occurring at nodes 7 (2 plants), 8 (5plants), 9 (7 plants), and 10 (4 plants). In keeping with ar-chitectural pattern 5 for the species, once a plant began toproduce tendrils, they were present at all subsequent nodes.

Discussion

This is the first developmental study of a species of Rhoi-cissus, and when combined with previous work on othergenera, it adds to our understanding of developmental mor-phology in the Vitaceae. This can best be accomplished by

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Fig. 3. Schematic diagram of a typical inflorescence showing therelatively sparse numbers of dichasia.



comparing these results with those for other species and byrelating this to phylogenetic hypotheses for the family.

Shoot developmentThe method by which the unique leaf-opposed tendril and

inflorescences are produced in the Vitaceae has been the

subject of much controversy (see Gerrath and Posluszny1988), Gerrath et al. 1998), and literature cited within) be-cause the shoot architecture would argue for sympodialgrowth, but actual shoot ontogeny in the first species studiedwas shown to be monopodial, with the shoot apicalmeristem producing both leaves and uncommitted primordia

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Fig. 4. Habit photographs of flowers and fruits. (a) Unopened flowers showing the petals (P) pushing through the calyx ring (K).(b) Petals dissected away from an unopened flower to reveal the stamens (A) and the base of the gynoecium (G). (c) Flower atanthesis showing how the petals reflex. Si, stigma and style. (d) Two flowers illustrating that floral development is not synchronous.On the left, the petals have protruded through the sepal ring (K) and form the main protection for the reproductive portion of theflower. The flower on the right is postanthesis and illustrates that petals and stamens fall off, exposing the pronounced gynoecial disc.(e) Fruits form in small clusters; they are green when unripe (B1) and turn dark purple when ripe (B2).



on its lateral flank (Gerrath and Posluszny 1988; Millington1966; Tucker and Hoefert 1968). More recently, it has beenshown that species in the Vitaceae differ in the manner bywhich they produce their uncommitted primordia, and exam-ples of all three modes of branching (monopodial,dichopodial, and sympodial) were demonstrated for differentspecies with the same shoot architecture (Gerrath et al.1998). However, sympodial branching, in which the shootapex bifurcates unequally, with the larger portion initiallybeing allocated to the structure that will ultimately appear tobe lateral and leaf opposed, has been found to occur only inR. digitata to date (Figs. 2a and 2b) (Gerrath et al. 1998).

The significance of these results in understanding theoverall evolution of the unique shoot architecture in the fam-ily is not yet clear. Shoot architecture of available herbariumspecimens of other species of Rhoicissus (Rhoicissus cunei-folia (Eckl. & Zeyh.) Planch., Rhoicissus rhomboidea(E. May) Planch., Rhoicissus revoilii Planch, and Rhoicissuserythrodes (Fresen.) Planch.) conformed to architectural pat-tern 5 (continuous tendrils and axillary buds) (Gerrath et al.2001). Although this might lead to the assumption that ourfindings for R. digitata can be extrapolated to other speciesin the genus, our shoot developmental information forR. rhomboidea indicated that in this species, the shoot apicalmeristem bifurcates almost equally, with the slightly largerportion given over to produce the new uncommitted pri-mordium (Gerrath et al. 1998). Thus, it appears that evenwithin a genus with shared mature shoot architecture, devel-opmental pathways may differ subtly between species. Wemust conclude that shoot architectural and developmentalpatterns are too variable within a genus to be useful from aphylogenetic standpoint.

Floral developmentFloral development characters have been used to test

phylogenetic hypotheses in many plant families based onmolecular information, for example, in the Fabaceae (Tucker2003). Although flowers in the Vitaceae are small, with onlysubtle distinctions between generic floral characters, floralcharacters are used to distinguish the genera (Süssenguth

1953), and so a similar strategy can be used successfully.Table 1 lists the known floral developmental characters forall species studied to date, including the data presented inthis paper. Figure 5 shows the generic relationships postu-lated by Ingrouille et al. (2002), based mainly on rbcL data.A second recent study (Rossetto et al. 2002), based on thetrnL(UAA) intron and the ITS1 region, did not provide auseful template for this study because they included too fewgenera common to those for which we had floral develop-ment data.

The monotypic genus Leea has always been considered tobe distantly related to the rest of the Vitaceae and has oftenbeen placed in its own family, Leeaceae (Süssenguth 1953;Cronquist 1981), although not by all authors (Dahlgren1980; Latiff 2001). Much of the reason for placing Leea inits own family was based on mature floral characters (Nair1968; Nair and Nambisan 1957). Although Gerrath et al.(1990) concluded that Leea guineensis shared the same fun-damental ontogenetic plan as species whose ontogeny wasknown in the Vitaceae, the fact that the ontogeny of so fewspecies had been followed, combined with the presence ofseveral unique derived features in Leea, warranted its contin-ued separation from the Vitaceae. Recent molecular datahave been used as the basis for placing Leea in the Vitaceae,although it is still considered to be basal to the rest of thefamily (Ingrouille et al. 2002).

Based on the information in Table 1, Leea does possess anumber of features that might be considered to be basal inthe Vitaceae. These include (i) inflorescence branches incompound dichasia, (ii) completion of initiation of all pri-mordia in a whorl before initiation of the next whorl begins,(iii) lack of petal fusion, and (iv) bisexual flowers. However,Leea is unique in the family in having a tricarpellate gynoe-cium. It also has a number of unique characters that could beconsidered to be derived, since they all occur as the result ofcontinued development of characters that begin as typical forthe Vitaceae. These include (i) laterally connivent stamens,(ii) secondary septa in the gynoecium, (iii) formation of anintercalary meristem below the points of insertion of the pet-als, stamens, and disc to form a floral tube, and (iv) further

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Inflorescence branches Precocious initiation Sepals Petals

Leea guineensis Compound dichasia None Individual No fusion

Ampelopsisbrevipedunculata

Compound dichasia None Individual No fusion

Rhoicissus digitata Compound dichasia Calyx ring (before all sepal primordia) Calyx ring No fusionCissus antarctica Compound dichasia Calyx ring (before all sepal primordia) Calyx ring No fusion

Parthenocissusinserta

Compound dichasia Calyx ring, petal/stamen primordium Calyx ring No fusion

Parthenocissusquinquefolia

Compound dichasia Calyx ring (before all sepal primordia) Calyx ring No fusion

Parthenocissustricuspidata

Compound dichasia Calyx ring (before all sepal primordia) Calyx ring No fusion

Vitis riparia Spiral, then compounddichasia

Inflorescence primordia before bracts,calyx ring, petal/stamen primordium

Calyx ring Postgenitalfusion toform calyptra

Table 1. Floral developmental characters in the Vitaceae.



elaboration of the gynoecial disc to form what has been re-ferred to as “staminodes” (Nair 1968; Nair and Nambisan1957). Thus, on the basis of floral ontogenetic data, Leea ap-pears to be related, but distantly so, to the rest of the family.

The proposed phylogeny (Fig. 5) (Ingrouille et al. 2002)shows Ampelopsis and Rhoicissus sharing a clade and as thenext most basal in the family. Our ontogenetic studies con-cur with this finding (Table 1) and show that the two repre-sentative species that we have studied differ in only a fewminor ways: (i) Ampelopsis brevipedunculata shows no evi-dence of precocious initiation of any whorls (although thestamens were initiated very shortly after the petal primordia)(Gerrath and Posluszny 1989b), whereas the calyx ring inRhoicissus is well developed and shows precocious initia-tion, and (ii) the nectary disc in Ampelopsis is distinct fromthe ovary base, unlike in Rhoicissus. Thus, Rhoicissus ap-

pears to have at least one derived feature, unlike Ampelop-sis. For the most part, however, their patterns of floral on-togeny are very similar, again concurring with the phylog-eny of Ingrouille et al. (2002).

Floral development in Cissus antarctica is very similar towhat we found for A. brevipedunculata (Gerrath and Pos-luszny 1994) and is distinguished from R. digitata mainly onthe basis of its disc morphology (Table 1). Whether it is theappropriate exemplar for the genus is in doubt based on therecent phylogenetic study by Rossetto et al. (2002), whichindicated that C. antarctica may belong to a clade that in-cludes Vitis rotundifolia. Unfortunately, the floral ontogenyof V. rotundifolia has not been studied, so comparisons can-not be made at this time.

The proposed phylogeny published by Ingrouille et al.(2002) places Vitis and Parthenocissus (Parthenocissushimalayana and Parthenocissus quinquefolia) in a grade inwhich Vitis does not appear to be monophyletic. Again,V. rotundifolia was used as one of the test species, and soclearly, more work needs to be done to clarify this portion ofthe proposed phylogeny. Parthenocissus is the only genusfor which there is good documentation of floral ontogeny formore than one species (Gerrath and Posluszny 1989a; Wil-son 2002) (Table 1). These studies indicated that as wouldbe expected, floral development is very similar among thethree species studied, but that there are also differences. Allthree species share precocious initiation of the calyx ring.However, gynoecial initiation in Parthenocissus inserta dif-fers from that in the other two species in that separateprimordia are not initiated prior to formation of the gynoe-cial ring. Likewise, only P. inserta shows precocious initia-tion of stamen primordia via a common petal–stamenprimordium. Parthenocissus tricuspidata is unique in that ithas a flattened stigma. Although P. quinquefolia andP. inserta share a similar disc morphology, only P. quin-quefolia produces large amounts of nectar. Late in develop-ment, the disc lobes of P. tricuspidata extend to form a moreexaggerated nectary structure. All these differences occurlate in floral ontogeny, which would be expected in closely

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Stamens Gynoecium Disc Nectar Bisexual Source

Laterallyconnivent

Ring, tricarpellate,secondary septum(six locules)

“Staminode” replacesnectary disc

No Yes Gerrath et al. 1990

No fusion Ring, then bicarpellate Distinct “moat” Yes Yes Gerrath andPosluszny 1989b

No fusion Ring, then bicarpellate Widening of ovary base Yes Yes This paperNo fusion Ring, then bicarpellate Distinct widening of

ovary baseYes Yes Gerrath and

Posluszny 1994No fusion Ring, then bicarpellate Indistinct from ovary Some Yes Gerrath and

Posluszny 1989aNo fusion Five bumps, then ring,

then bicarpellateIndistinct from ovary Yes Yes Wilson 2002

No fusion Five bumps, then ring,then bicarpellate

More distinct lobes Some Yes Wilson 2002

No fusion Ring, then bicarpellate Ring at ovary base No, scent? Dioecious Gerrath andPosluszny 1988

Fig. 5. Proposed phylogeny of the Vitaceae, based on rbcL data,and redrawn from Ingrouille et al. (2002).



related taxa (Tucker 1984). Unfortunately, within Partheno-cissus, there is no current phylogenetic hypothesis on whichto pin these differing character states.

Vitis riparia appears to have the greatest number of de-rived features: (i) spiral inflorescence branches followed bycompound dichasia, (ii) several instances of precocious pri-mordium initiation (inflorescence primordia, calyx ring,petal–stamen primordium), (iii) postgenital fusion of the pet-als to form a calyptra, (iv) a distinct nectary disc, but withno nectar production, and (v) dioecy brought about by fail-ure of full development of either the androecium or thegynoecium (Gerrath and Posluszny 1988). This wouldappear to concur in a general way with the phylogeny pro-posed by Ingrouille et al. (2002). However, given the possi-bility that Vitis is not monophyletic (Ingrouille et al. 2002;Rossetto et al. 2002), the full floral ontogeny of more spe-cies of Vitis needs to be completed.

Despite the economic importance of commercial grapes,the Vitaceae remains an understudied family from a botani-cal perspective. This is unfortunate because it appears thatthe family has been isolated from the rest of the core rosidsfor some time, and its placement is still uncertain (Soltis etal. 2003). This study is part of an ongoing series in whichwe will continue to use floral development as a tool for un-derstanding the characters themselves and the relationshipsbetween the species and genera that carry them.

Acknowledgements

We would like to express our thanks to Joe Gerrath fortranslations of Süssenguth (1953) and to the personnel at theRijksherbarium, Leiden, for their assistance. We would alsolike to thank the staff at the University of Northern Iowa Bi-ology Botanical Center for their excellent plant care. Thisstudy was supported by the Natural Sciences and Engi-neering Research Council of Canada (U.P.) and the Univer-sity of Northern Iowa College of Natural Sciences (J.M.G.).

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