inflorescence types - mios journalmiosjournal.org/journal/2013/03/miosj201303_02-08.pdf · 6 spike:...

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Ed. Note: Back in (nearly) the ancient history of this publication, a few offerings

about botanical terms were published for novice members. The following one

originally appeared in Vol. 3(7): 5-7 (2002).

In ordinary conversation most humans tend to generalize, and use “slang” words

and clichés, but the language of science is exact, descriptive, and meticulous. If the

words seem strange, the problem is not with science, but with the habit of careless-

ness in general conversation. These definitions, from July, 2002, are reviewed,

updated, and embellished particularly for the benefit of newer members.

Inflorescence Types

Inflorescence: “the arrangement of flowers on a floral axis; a floral cluster.”

Inflorescence Types

General: Before discussing inflorescences, another term, rachis, needs to be de-

fined. A rachis (ráy-

kiss) is (1) the axis

of a compound leaf

or fern upon which

the leaflets are at-

tached; or (2) the

major axis of an

inflorescence. That

said, Correll and

Johnston (1970)

define the term in-

florescence as “the

flower cluster of a

plant, or, more cor-

rectly, the disposi-

tion of the flowers on an axis.” Dressler (1981) simplifies this to “the flower (if

solitary) or flower cluster of a plant.” More simplistically, the inflorescence is that

specialized structure that holds the flowers. However, there are different types of

inflorescences, and at this point, specialized terminology enters the scene. Intro-

ducing this plant part, six basic types of inflorescences are shown here (Fig. 1).

These are not all the inflorescence types, but they’ll do for a start. In addition, in-

florescences are differentiated as terminal or lateral by the location from which

they arise on the plant. An inflorescence produced at the apical end of the shoot or

pseudobulb is called terminal. Lateral inflorescences arise from nodes near the

pseudobulb base, the sides of stems, or from leaf axiles or opposite leaf axiles.

It should be understood that just because one species of a genus exhibits a cer-

tain inflorescence type or flowers terminally or laterally, not all members of the

genus necessarily have the same habits. Maxillariella tenuifolia, for example, pro-

duces single flowers, but Camaridium (used to be Maxillaria) densa produces its

flowers in a panicle. The key here is that we are trying to define the inflorescence

itself, not trying to generalize it to any genus. Remember: just because a species of

The MIOS Journal 14(3): 2-8. 2013. Ferry, R. J.: Inflorescence Types.

Fig. 1. Diagrammatic representation of inflorescence types.

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Paphiopedilum, Maxillaria, or a species of another genus is mentioned as bearing

flowers a certain way, doesn’t mean all members of a genus will do the same.

Single: The single type of inflorescence is seen in Paphiopedilum species as well

as in members of Lockhartia, Lycaste (Fig. 2), Maxillaria, Miltonia, and other

orchid genera. In passing,

note that the Lycaste conso-

brina provides an example

of single flowering as well

as demonstrating lateral

flowering; arising from the

pseudobulb base. As an

aside, it may also be noted

that L. consobrina flowers

begin opening prior to the

new vegetative growth

sprouting. Note also the

rather dehydrated condition

of the pseudobulbs. In their

normal annual growth cycle,

the vegetation grows; the pseudobulb then forms below; and then the leaves ma-

ture, wilt, and are discarded. The plant then enters the “winter” or dry season as

only a cluster of pseudobulbs. These gradually dehydrate and as their internal sug-

ars coalesce, flowering is initiated with the onset of the wet-season or “spring

rains. The flowers open and are hopefully pollinated, followed soon by the new

vegetative growth. As the “wet-spring” gives way to the slightly drier summer

season, the seed capsules mature. As the “winter-dry season” sets in, the capsules

dehisce and the powdery seeds are blown to new locations to (hopefully) sprout

with the onset of the following “spring-wet” season.

Head or Composite: The term “head” should actually

be labeled composite. It may appear to be seen in a

few orchid species where the flowers are densely

packed on the inflorescence, but orchids don’t utilize

the composite mode of flowering. Dicots do. Members

of Asteraceae (the Aster or Sunflower family) and the

Fabaceae (Bean or Legume Family) are good exam-

ples. In the monocot Orchid family, we don’t see the

composite flowering form, but it’s included here mere-

ly as an example of one of the inflorescence types. Some orchid species do cluster

their flowers terminally, but they do so as an umbel modification or a panicle, not

a head or composite.

A ready example of a head inflorescence is seen in Red Clover (Trifolium prae-

tense L.), a widespread wildflower (a member of Fabaceae, the bean family; Fig.

3). Members of the Aster (sunflower) family also produce the classic composite or

“head” which actually contains many individual flowers, each of which produces a


Fig. 2. Lycaste consobrina. Note the lateral flowering from the base of the pseudobulb.

Fig. 3. Red Clover. (Trifolium repens L.)

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single seed. The yellow “petals” around a sunflower head’s circumference are not

petals at all, but ray

flowers. In older books

the reader may run

across the name

“Compositae” for the

Family Asteraceae, and

“Leguminosae” for the

Family Fabaceae .

These are obsolete

terms for these families.

Several years ago, the

international congress

of botanists agreed to

change these family

names as listed in the

International Code of

Botanical Nomenclature

in order to reflect

a more correct

viewpoint of

each family.

Thus, correctly

speaking, the

Asteraceae is the

Aster (not Sun-

flower) family

and Fabaceae is

the Bean (not

Legume) family.

Umbel: This type

of inflorescence

is well illustrated

by members of

the Asclepidaceae (Milkweed family), Gentianaceae (Gentian family), and Apocy-

anaceae (Dogbane family). Observing closely, it will be noted that the inflorescence

is actually a group of flower clusters or umbels held terminally on the stem. Casual-

ly, the whole inflorescence is sometimes referred to as an umbel, but it might be

better termed an “umbel of umbels” or a “compound umbel.” This type of inflo-

rescence is typically seen in the “Butterfly weed” (Fig. 4).

Another attractive example of the umbel type of inflorescence may be seen in the

flowers of an aquatic, The “Floating Heart,”Nymphoides aquatica (Gmel.) Ktze.

(Fig. 5). This perennial is known from ponds, lakes, and slow streams in Florida

and coastal plain of Georgia west into Louisiana and eastern Texas. One suspects it


Fig. 4. Asclepias lanceolata (Asclepidaceae). (Butterfly Weed, Chigger Weed) Umbel type inflorescence.

Fig. 5. Nymphoides aquatica (Gmel.) Ktze. (Gentianaceae). (“Floating heart”) Umbel inflorescence

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would readily acclimate in ponds in the Rio Grande Valley. In some orchid spe-

cies, occasionally the axis of a spike can be leaf-like, and the flowers are borne on

a structure called a phylloclade.

This umbel modification, the

umbellate raceme, occurs in

Bulbophyllum (Fig. 6), Cir-

rhopetalum, Epidendrum, Mal-

axis (Fig. 7), and Microstylis.

Asclepias lancolata and other

members of the milkweed fami-

ly are frequented by Monarch

butterflies which also lay their

eggs on the plants. As the cater-

pillars dine on the leaves, they

ingest the poisonous milky sap.

This otherwise poisonous sap

doesn’t harm the caterpillars,

and it is passed on to the ma-

ture butterflies. As a result, a

young bird eating a Monarch

butterfly very shortly discovers

that eating this particularly col-

ored insect causes a severely

upset stomach. The result is the

young bird learns to leave mon-

archs alone! The Viceroy but-

terfly’s caterpillar does not dine

on milkweeds, and hence the

Viceroy remains a tasty meal

for a bird. However, its colora-

tion imitates the Monarch well

enough to deceive the bird-

predators, and it gets left alone

as well. This phenomena is

known as Batesian mimicry. By

the way, as a note to humans

inclined to examine the flowers

of “Butterfly weed” and handle

them in the wild: they’re also

known as “Chigger weed,” and

an encounter with chiggers that

have gained access to the hu-

man body, particularly in the

underarm, joint, and groin areas

is not soon to be forgotten!


Fig. 7. Malaxis corymbosa Umbel type inflorescence. 35mm slide #040900-1. Km 17-20 area, ca. 1500m.

Mexico, Nuevo León, Hwy Santiago Laguna Sanchez.

Fig. 6. Bulbophyllum odoratissimum. Darjeeling, India Umbel type inflorescence.

Photo: R. Yonzone used by permission.

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Spike: Spikes resemble racemes, but bear sessile flowers (sessile: without a stalk;

sitting directly on its base). It’s common

to hear orchidists speak of a “flower

spike,” or a plant “spiking,” “being in

spike.” At the same time, purists have

been known to visibly cringe or make a

smug “side comment” about how

“orchids don’t spike,” or “it’s not a spike,

it’s a panicle,” or some other such put-

down. In actuality, the purists are partly

correct in that many of the epiphytic or-

chids don’t spike. Spikes are uncommon

in the Orchidaceae, and there are species

of Orchis in which inflorescences in the

bud stage appear to be racemes, but fol-

lowing pollination assume the appearance

of a spike because their swollen ovaries,

which looked like peduncles prior to fer-

tilization, have now become recognizable

as such. As well, although some of the

flower in Spiranthes (Fig. 8) display a

bract, they are held tightly and are said to

be sessile. The sum total is simply this:

don’t look for spikes as an orchid inflo-

rescence pattern, but realize that they do

exist in some genera

Raceme: A raceme is an unbranched, indeterminate inflorescence, in which the

individual flowers are borne on pedicels along

the main axis. In this case, the main axis = ra-

ceme = rachis. Most orchids flower racemose

(meaning “on a raceme” or “raceme-like”). An

example may be seen in the showy unbranched

Specklinia grobyi racemes displaying flowers

one after another in a long arch. What they lack

in size, they make up for in quantity (Fig. 9). ]

In a raceme, the flowers open from bottom to

top or—said another way—from closest to the

plant outward (it’s called acropetal flowering).

In a panicle, it’s reversed, with the outermost

flowers open first (basipetal flowering).

For the typical orchid grower in southern Tex-

as, the two most recognizable examples are of

hybrids of the genera Dendrobium and

Phalaenopsis, seen bearing long sometimes

erect, usually arching racemes. One relatively


Fig. 8. Spiranthes cernua. Inflorescence spikate. DSC_4926a Thur-01Nov-12.

USA; Texas Fayette County.

Fig. 9. Specklinia grobyi. raceme. (actually, 15 racemes on this plant)

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small spring-flowering species is Dendrobium lindleyi (Fig. 10). Year ago, it was

more commonly known as Den. aggre-

gatum i t gained the nickname

“Dendrobium aggravation” from or-

chidists who had difficulty getting it to

flower “exactly when they wanted it to

do so.” Racemes locally include those

of Den. Jaquelyn Thomas (Fig. 11),

Den. Nellie Sugii (Fig. 12), and others.


Above: Fig. 10. Dendrobium lindleyi. raceme. DSC_0730 Mon-01May-06

Right: Fig. 11. Den. Jaquelyn Thomas raceme. Pl#220305-4 DSC_3020. Thur-03Aug09.

Clone: ‘Uniwai Mist’

Below: Fig. 12. Pl#.091105-3. Den. Nellie Sugii.

DSC_3023 (raceme) Thur-03Aug09.

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Panicle: The panicle is a rachis with branches. As one definition states it:

“pedicillate flowers are borne upon the secondary branches.” True, but this is not

necessarily the whole story. Oncidium sphacelatum panicles have primary branch-

es, and then may have secondary branches and even tertiary branchlets! With a

rachis of over 2 meters long and branchlets fronding out to 60 cm. (2 feet!) on ei-

ther side, and all bearing flowers, it makes for a spectacular display,... and that’s a

single panicle on a plant that may carry as many as fifteen, twenty, or more!

The panicle inflorescence confers an advantage to the plant over the raceme

form in that a raceme can only carry so many flowers. Because of its branching, a

panicle can carry many more flowers, and more flowers mean greater chances for

more seed capsules and hence, greater “plant hope” for more orchid seedlings! In

2002, the Encyclia belizensis, subsp. parviflora alba (Fig. 13) managed to bear

only three panicles, but these carried a total of 194 flowers! In the figure above the

forty inflorescences of 2011 carried orders of magnitude more flowers! In the

spring of 2012, counting was stopped at 72 individual panicles! Now, as spring

looms for 2013, there will be one more count and the plan is then to divide this

large monster! The paniculiform inflorescence conveys not only a reproductive

advantage to the plant, but, for the orchid lover, many more flowers per plant.

For the orchidist, the main compromises are usually the size of the pocketbook

gauged against the size of the greenhouse, but with other considerations taken care

of, the choices may come down to whether one wants a few very large flowers or a

great many smaller ones, or perhaps which types and sizes of plants and types of

inflorescences one prefers.

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Fig. 13. Pl#290496-1. Encyclia alata sub species parviflora. Plant carrying 40 panicles. DSC_4155 Mon-23May-11.

inflorescence types - mios journalmiosjournal.org/journal/2013/03/miosj201303_02-08.pdf · 6 spike:...

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