Inflorescence Terminology (Part 2)

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Inflorescence Terminology Part 2

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6. Cyathium: Inflorescence Of The Euphorbia Family

One of the largest genera of flowering plants is Euphorbia with approximately 2,000 species. This enormous genus belongs to the very diverse euphorbia family (Euphorbiaceae) with at least 7,500 species. The variation within this genus is astonishing, from low-growing garden weeds called spurges to giant, cactus-like succulents that rival in size our North American sahuaro and organ-pipe cacti. South African euphorbias have evolved succulent, spine-covered stems that greatly resemble North American cacti, a biological phenomenon known as convergent evolution. It is difficult to believe that all these diverse forms belong to the same genus as the showy garden euphorbia called poinsettia (E. pulcherrima) until you carefully examine the blossom. The showy, red, modified leaves of poincettia are not petals. In fact, they are not even part of the true flowers. They surround clusters of small, greenish, cup-shaped structures called cyathia. Each cyathium is actually a flower cluster or inflorescence containing unisexual, apetalous male and female flowers. The inconspicuous male flowers occur in clusters and are reduced to a single red stamen, while the female flower consists of a single ovary (pistil) on a stalk (pedicel). In poinsettia the ovary is hidden within the cyathium, but in other species the ovary protrudes out of the cyathium at maturity. The rim of the cyathium also bears one-several, greenish nectar glands that are attractive to insect pollinators. In some species the glands are subtended by petal-like bracts (petaloid appendages). Poinsettias typically have only one greenish gland per cyathium and no petaloid appendages. This flower plan is quite different from the typical floral plan, but it is the basic theme in virtually all members of the amazing genus Euphorbia. It should be noted here that some authorities place the prostrate, herbaceous euphorbias (called spurges) with C-4 photosynthesis in the genus Chamaesyce.

Poinsettia (Euphorbia pulcherrima) in full bloom at Christmas time in southern California. Left: Bright red modified leaves (A) surround a central cluster of greenish-yellow flower clusters called cyathia. Right: Each cup-shaped cyathium (B) contains a cluster of red stamens (D) which are the male flowers. Inside each cyathium is a hidden female flower (not shown) consisting of a single, minute ovary. The rim of the cyathium bears a greenish-yellow nectar gland (C).

Chamaesyce albomarginata, a prostrate, native euphorbia (spurge) that grows throughout dry chaparral hillsides and inland valleys in southern California. A: Cup-shaped cyathium (involucre) containing several minute stamens (male flowers) and a pistil or gynoecium (female flower) with a large ovary on a long stalk. B: Petaloid appendage extending from the rim of cyathium. C. Oval gland at the base of a petaloid appendage. D. Ovary of a female flower on a stalk that extends out of the cyathium. The ovary is glabrous (without pubescence) and develops into a multiseeded dry fruit or capsule. E. White membranous scale composed of united stipules at the base of the leaves.

The Remarkable Eurphorbia Family (Euphorbiaceae)

7. Syconium: Inflorescence Of The Figs (Ficus)

In a strict botanical sense fig "fruits" are actually inside-out flower clusters (inflorescences) called syconia. They are hollow, fleshy structures composed of modified stem (peduncular) tissue, lined on the inside with hundreds of minute flowers. At one end is a small opening (ostiole) lined with dense, overlapping scales. Calimyrna syconia contain only female flowers and must be pollinated in order to ripen. Each tiny flower consists of a five-parted calyx and an ovary with a long style. Following pollination and fertilization the ovaries develop into minute one-seeded drupelets with a hard inner layer (endocarp) surrounding the seed. The seed-bearing drupelets produce the superior nutty flavor and crunch. Without pollination Calimyrna syconia fail to ripen and drop from the branches.

Left: A view inside the syconium of a rustyleaf fig (Ficus rubiginosa). The syconium is lined with numerous apetalous, unisexual flowers. Right: The unisexual flowers of Ficus palmeri. The male flower consists of a stamen subtended by sepals. Female flowers consist of a pistil (gynoecium) subtended by sepals. Using its threadlike ovipositor, the female fig wasp can oviposit through the short style but not the long style. Therefore, the ovaries of short-style flowers contain a wasp larvae, while the ovaries of long-style flowers contain a seed.

Syconia Of Common Edible Fig (Ficus carica):

1. The syconium is a complex inflorescence (flower cluster) consisting of a hollow, fleshy structure (peduncular tissue) lined on the inside with numerous tiny unisexual flowers. The ripe syconium is not a true fruit in the strict botanical sense. It is actually a fleshy, flask-shaped, modified stem lined on the inside with many tiny one-seeded fruits. The mature fig syconium is also called a multiple fruit because it is composed of numerous ripened, seed-bearing ovaries derived from numerous female (pistillate) flowers.

Stamen-Bearing Syconium Of The Male Caprifig
Female Syconium Packed With Long-Style Flowers

2. Ficus carica has 2 sexual forms, the "male" caprifig and the female tree (edible fig). Caprifig trees are monoecious with separate male (staminate) flowers and short-style female (pistillate) flowers within the syconia. It is functionally male because it produces pollen. The caprifig syconia also contain wasp larvae inside the ovaries of female flowers because the egg-laying wasp is able to oviposit through the short styles into the ovaries of these flowers. Since a hungry wasp larva occupies each ovary, fig seeds generally do not develop.

3. Edible fig syconia contain only long-style female flowers. Seeds develop within the ovaries of these flowers since the styles are too long for the female wasp to oviposit through. Her ovipositor is not long enough to penetrate the ovaries of these flowers so she does not deposit an egg. Fig seeds develop inside the ovaries of long-style flowers since there is no larva to eat them. Since functional male trees are bisexual (hermaphroditic), Ficus carica is considered gynodioecious rather than dioecious.

NYBG Steere Herbarium Definition of Gynodioecious: Sexual condition of a species that bears pistillate flowers on some plants and bisexual flowers or staminate flowers as well as pistillate flowers on other plants. The important word here is "or" rather than "and" [e.g. Fig (Ficus) & Mulberry (Morus)].

Links About Figs & Fig Wasps

Fig Trees Of The Holy Land
Strangler Figs and Banyan Trees
Evolution Of Dioecious Fig Species
Ficus dammaropsis In New Guinea
Amazing Fig/Fig Wasp Relationship
Calimyrna Fig & Its Pollinator Wasp
Summary Of Common Fig Life Cycle
Cauliflory In Tropical Species Of Figs
Pollination Patterns In Dioecious Figs
Do Fig Wasps Induce Gall Formation?
Sex Determination In The Common Fig
Sexuality and Political Correctness In Figs
Petrified Fig Syconium From The Cretaceous
Grass Jelly From Creeping Fig (Ficus pumila)
 Nonpollinator Fig Wasps With Long Ovipositors 

8. Capitulum: Inflorescence Of The Sunflower Family

A capitulum or head, the characteristic inflorescence of the sunflower family (Asteraceae). Depending on the tribe, the inflorescence may consist of ray flowers, disk flowers, or both ray and disk flowers. The ovary of each flower is situated below the attachment of the corolla and stamens, a condition referred to as epigynous or inferior. This is the largest family of flowering plants with approximately 24,000 species. The variation in disk and ray flowers alone is astonishing.

Close-up view of a portion of the large flowering head of a sunflower (Helianthus annuus) showing an outer ring of large, strap-shaped (petal-like) ray flowers surrounding a dense mass of small, tubular disk flowers. The ovaries of the disk flowers ripen into the striped achenes sold in markets as sunflower seeds. The entire head is subtended by green, overlapping bracts called phyllaries.

The Asteraceae: World's Largest Plant Family
Fruits (Achenes) Of The Sunflower Family

Inflorescence Definitions

  • Cyathium: A cup-shaped involucre bearing several minute stamens (male flowers) and a pistillate flower consisting of an ovary on a long stalk (pedicel). The rim of the cyathium often bears one or more nectar glands and petaloid appendages. This is the characteristic inflorescence of the genus Euphorbia(and Chamaesyce) in the euphorbia family (Euphobiaceae).

  • Syconium: A hollow, spherical or flask-shaped inflorescence lined on the inside with numerous minute, apetalous, unisexual flowers. Male flowers consist of one to five stamens, while female flowers consist of a single pistil (gynoecium) with a long or short style. The flowers are pollinated by minute symbiotic female wasps that enter the syconium through a pore (ostiole). This is the characteristic inflorescence of remarkable figs in the genus Ficus (Moraceae) which includes an estimated 1,000 species.

  • Capitulum (Head): A short, dense inflorescence of sessile flowers attached to a common receptacle. This is the characteristic inflorescence of the sunflower family (Asteraceae). Some members of the Proteaceae also produce flowers in a dense cluster resembling a head.

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