Botany 115 Terminology

Flower Terminology Part 2

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Inflorescence Terminology Part 1
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7. Shapes Of Flowers


Left: Pacific madrone (Arbutus menziesii), an evergreen tree with smooth red bark that is native to forests of the Pacific coast of North America. It occurs in isolated (disjunct) populations in the mountains of southern California and northern Baja California. Arbutus peninsularis is endemic to mountains of the Cape region in Baja California. Another Mexican madroņo (A. xalapensis) grows in mountainous regions of Sinaloa and Chihuahua south through Veracruz and Oaxaca to Guatemala. Right: The urn-shaped (urceolate) flowers of the European strawberry tree (A. unedo) are typical of madrones, manzanita (Arctostaphylos) and other members of the heath family (Ericaceae).


See Edible Berries of Strawberry Tree

8. Shapes Of Flowers (Cont.)

Papilionaceous Flower Of Fabaceae (Legume Family)

Family Fabaceae--Subfamily Papilionoideae:

A dissected flower of Erythrina crista-galli showing all the major perianth segments removed from their attachment inside the calyx. The five petals consist of one large, oval banner or standard, two elongate keel petals that are fused together enclosing the stamens, and two reduced wings. Nine stamen filaments are united into a sheath that surrounds the pistil. One stamen filament is separate from the fused nine, a condition referred to as diadelphous. A drop of nectar is secreted at the base of the petals inside the calyx. At maturity the banner is widely separated from the keel petals, thus making the nectar fluid at the base of the petals (within the calyx) readily available to short-billed perching birds. Erythrina species pollinated by hummingbirds have elongate, tubular blossoms.

In true papilionaceous flowers (subfamily Papilionoideae), the upper petal is outside the lateral petals in the bud. This subfamily includes most members of the Fabaceae, including Dalea (smoke tree), Lupinus (lupine), Lathyrus (sweet pea), Erythrina (coral tree), Robinia (black locust) and Astragalus (locoweed).


The Pollination & Dispersal Of Coral Trees

Family Fabaceae--Subfamily Caesalpinioideae:

Members of the subfamily Caesalpinioideae have flowers that are bilateral, typically with five distinct petals, upper petal (banner) enveloped in the bud by the lateral wings. This subfamily includes Cassia (senna), Cercis (redbud), Bauhinia (orchid tree), Cercidium (palo verde), Parkinsonia (Jerusalem thorn), Caesalpinia (brazilwood), Haematoxylum (logwood), Ceratonia (carob), Tamarindus (tamarind) and Delonix (royal poinciana).

The orchid tree (Bauhinia variegata) native to India and China. The beautiful blossom superficially resembles an orchid. Although it is truly a legume, it is not papilionaceous. The upper petal is enveloped in the bud by the lateral wings.

A. Jerusalem thorn or Mexican palo verde (Parkinsonia aculeata), a tree native to deserts of Arizona and Baja California. B. Brazilwood (Caesalpinia echinata), a tree native to Brazil and one of the important dyewoods of the 1600s. The flowers are bilateral (irregular) but not truly papilionaceous.


See Logwood and Brazilwood

Family Fabaceae--Subfamily Mimosoideae:

Red powder puff (Calliandra haematocephala) native to Bolivia. Members of the subfamily Mimosoideae have flowers with radial symmetry, small, inconspicuous corollas and numerous, showy stamens. The flowers are typically in many-flowered heads or spikes. This subfamily includes Acacia (wattle), Albizia (silk tree), Samanea (monkeypod), Prosopis (mesquite) and Calliandra (powder puff).

Myrtaceae: Eucalyptus


The bisexual flowers of Eucalyptus polyanthemos showing the cylindrical cap (operculum) that separates to expose a mass of white stamens which surround the female pistil. The majority of flowering plant species have fewer than 20 stamens.


See Spectacular Flower of Eucalyptus macrocarpa

9. Flower Symmetry

10. Ovary Position

11. Placentation

Cross section of the ripened ovary (fruit ) of a bell pepper (Capsicum annuum) showing three locules (chambers) and axile placentation. The central region where the seeds are attached is the placenta. In hot chile peppers, the placental region contains up to 89 percent of the alkaloid capsaicin. This alkaloid causes a burning sensation when it comes in contact with the sense receptors in your tongue. Capsaicin is produced by a dominant gene. Since bell peppers are homozygous recessive for this trait, they do not produce capsaicin. Depending on the cultivar, green bell peppers ripen into bright shades of yellow, orange and red.


See Wayne's Word Article About Chile Peppers

12. Typical Flower Of The Grass Family (Poaceae)

In herbaceous (nonwoody) grasses, such as wheat, rice, barley and oats, each leaf has a basal sheath that envelops the grass stem (culm) down to its point of origin (node). At the upper end of each culm sheath is the actual leaf blade, which typically extends away from the culm. At the junction of the sheath and blade is a small, membranous scale called the ligule. Minute projections at the base of the leaf blade are called auricles. Grass leaves grow from an intercalary meristem at the base of the sheath in the node region. This is why the tranversely cut blades of grass plants in your lawn grow upwardly, even though you mowed them off the previous week. The meristematic region of herbaceous annual and perennial grasses is at the base of the leaves and continually produces more leaf tissue. This is undoubtedly an adaptation to grazing animals which could destroy the grass plant if the vulnerable growth regions were apical rather than basal. Flowering (seed-bearing) stems of cereal grasses develop from apical meristems that generally do not resprout if the peduncle (flower stalk) is severed. Annual grasses (including many weedy grasses in San Diego County) die following their blooming cycle. Perennial grases die back to the rhizome and resprout the following year. The structure and growth of bamboo leaves is very different from herbaceous grasses. It is explained in the Wayne's Word article about bamboo.

Annual blugrass (Poa annua), a common naturalized weed in southern California. The leaf blade extends down the culm as an enveloping sheath to a slightly enlarged point of attachment on the culm called the node. The internodes of grass stems are typically hollow. In fact, hollow bamboo culms have many uses, including blowguns, flutes and the transport of water. At the junction of the leaf blade and culm sheath is a small scalelike ligule. The floret consists of two bracts called the palea and lemma. Within the floret is the apetalous, bisexual grass flower consisting of a gynoecium (pistil) and three stamens (androecium). Following pollination and fertilization, the ovary develops into a one-seeded fruit called a grain or caryopsis. In some grasses, the minute remnants of perianth segments called lodicules are visible at the base of the ovary. Grasses are typically wind-pollinated, although some species have cleistogamous, self-pollinated flowers that remain closed within the bracts of the floret.

Note: A rather obscure characteristric used in the Jepson Manual key to grasses is the term "callus." This is a slight thickening (enlargement) at the connection point (junction) between the lemma and the main axis (rachilla) of a spikelet. In the naturalized Poa annua the callus is glabrous, while in the native P. bolanderi the callus is pubescent with cobwebby hair. This requires very careful examination. Although the callus of P. annua is glabrous, the base of the lemma has cobwebby pubescence.

Littleseed muhly (Muhlenbergia microsperma), showing a cleistogamous spikelet at the base of a lower leaf sheath. Several self-pollinated spikelets may be contained within a tightly-rolled leaf sheath, which readily disarticulates from the plant at maturity. The grains from these cleistogamous spikelets are larger than grains from the terminal spikelets. This species is a native, clumping, annual grass in dry areas of coastal sage scrub and creosote bush scrub in southern California.



Littleseed muhly (Muhlenbergia microsperma). A basal leaf sheath has been split apart to expose two cleistogamous spikelets. These are fertile, self-pollinated spikelets that are completely contained within the tightly-rolled leaf sheath.



Deergrass (Muhlenbergia rigens) in a grassy meadow of the Cuyamaca Mountains, San Diego County. This native perennial bunchgrass is relatively common in canyons and mountain meadows of southern California. It was widely used by the Cahuilla people for making baskets.


General structure of a coiled basket. Bundles of flowering stems (culms) of deergrass (Muhlenbergia rigens) were commonly used by the Cahuilla and other tribes for the foundation (primary coils) of the basket, around which the secondary coils were tightly wrapped. Basketbush (Rhus trilobata) was commonly used for the secondary coils, with intricate designs made from brown coils of rush culms (including Juncus acutus, J. effusus, J. lesueurii and J. textilis). Sometimes the rush culms were dyed to produce various color patterns. Other plants were also used for basketry in the American southwest, including willow (Salix), beargrass (Nolina microcarpa), yucca (Yucca elata) and devil's claws (Proboscidea parviflora).


The Mysterious Flowering Cycle Of Bamboo
Bamboo: A Truly Remarkable Giant Grass
Devil's Claw: A Hitchhiker On Big Animals



Plantlets (bulblets) of Poa bulbosa, a perennial bluegrass with florets that develop into small bulblets while still attached to the inflorescence. This species is propagated by bulblets rather than ungerminated grains. It was intoduced from Europe and has spread throughout the northern United States and mountainous regions of California.

13. Grasses, Sedges and Rushes Compared

Plants of the sedge family (Cyperaceae) and rush family (Juncaceae) superficially resemble grasses; however, they are quite different from true grasses. Like grasses, they have small flowers without colorful petals; however, they do not have many of the unique floral characteristics of grasses, such as the palea, lemma, glume and grain (caryopsis). The ovary of sedges develops into an achene, while the ovary of a rush (Juncus) develops into a many-seeded capsule. Like grasses, sedges and rushes are important grazing plants for herbivorous animals and provide valuable nesting sites in wetland habitats. Sedge and rush stems often contain spongy aerenchyma tissue with abundant air spaces. This allows air to reach the root systems which are often submersed in water-logged mud. Rush stems (Juncaceae) are generally circular in cross section, while the stems of sedges (Cyperaceae) are typically three-sided (triangular). A few species in the Cyperaceae are used by people. The fibrous stems of papyrus (Cyperus papyrus) are an ancient source in paper dating back more than 5,000 years, and the crispy corms of water chestnut (Eleocharis dulcis) are an important component in many Asian entrees.

A comparison of the typical flowers of the grass family (Poaceae), sedge family (Cyperaceae) & rush family (Juncaceae). In grasses, the individual flower is referred to as a floret. In the sedge family, each flower is subtended by a scalelike bract. Since the scalelike petals and sepals of the rush family are very similar in appearance, they are referred to as tepals. The ovary of a grass develops into a one-seeded grain (caryopsis). The ovary of a sedge develops into one-seeded achene, while the ovary of a rush develops into a many-seeded capsule.


See More Flower Details Of The Sedge & Rush Families

14. Flower Definitions

  • Papilionaceous: Characteristic flower of the subfamily Papilionoideae within the legume family (Fabaceae). The irregular (zygomorphic) flower is composed of five petals, including one banner petal or standard, two lateral wing petals, and two fused keel petals that enclose the gynoecium and stamens. In some species the ten stamens are all united by their filaments (monadelphous) or one stamen is free and the other nine are united (diadelphous).

Note: The legume family is the third largest family of flowering plants with nearly 20,000 described species. Only two families have more species, the orchid family (Orchidaceae) and sunflower family (Asteraceae). The legume family is subdivided into three subfamilies: Papilionoideae, Caesalpinioideae and Mimosoideae. The Papilionoideae have papilionaceous flowers, including many well-known legumes such as sweet pea (Lathyrus), alfalfa (Medicago), bean (Phaseolus), pea (Pisum), clover (Trifolium) and lupine (Lupinus). Flowers of the Mimosoideae consist of showy clusters of numerous stamens arranged in dense spikes or heads, and inconspicuous petals. Examples of this subfamily include mesquite (Prosopis), acacia (Acacia), fairy duster (Calliandra), silk tree (Albizia) and monkeypod (Samanea). The subfamily Caesalpinioideae contains a group of closely-related legumes which have flower buds with their upper petal enveloped by the lateral petals. [In the flower buds of most legumes, the upper petal (banner) is on the outside.] The mature flowers have radial symmetry with five spreading petals, unlike the irregular, pea-shaped (papilionaceous) flowers of subfamily Papilionoideae. The subfamily Caesalpinioideae includes many familiar trees and shrubs including poinciana or bird-of-paradise bush (Caesalpinia), orchid tree (Bauhinia), cassia (Cassia), carob (Ceratonia), palo verde (Cercidium), redbud (Cercis), royal poinciana (Delonix), logwood (Haematoxylum), Jerusalem thorn (Parkinsonia) and tamarind (Tamarindus).

  • Actinomorphic (Regular): Flower with radial symmetry because the perianth segments (petals and sepals) are similar in size and shape. This type of flower is divisible into equal halves along more than one plane.
  • Zygomorphic (Irregular): Flower with bilateral symmetry because the perianth segments are dissimilar in size and shape. This type of flower is divisable into equal halves along only one plane.
  • Superior: Refers to a ovary that is above the attachment of the petals, sepals and stamens, and is free from the receptacle. A perigynous ovary within a cup-shaped hypanthium is superior if it is completely free from the outer hypanthium.
  • Inferior: Refers to an ovary that is below the attachment of the petals, sepals and stamens. The hypanthium may be fused to the ovary wall or attached to the top of the ovary. The ovary of an apple is inferior because it is fused with a thick, fleshy hypanthium. Stamens, petals and sepals arise from the top of the hypanthium (on top of the apple).
  • Hypogynous: Below the gynoecium, referring to perianth segments and stamens that are attached directly to the receptacle at the base of an ovary.
  • Perigynous: Around the gynoecium, referring to perianth segments and stamens that are attached directly to the rim of a cup-shaped hypanthium that surrounds the ovary. In this case, the ovary is completely free from the outer hypanthium.
  • Epigynous: Above the gynoecium, referring to perianth segments and stamens that are attached to the top of the ovary or to the rim of a cup-shaped hypanthium that is attached to the top of the ovary.
  • Hypanthium: A cup-shaped structure surrounding the ovary and formed by a fusion of the bases of the perianth segments (petals and sepals). Some references state that the hypanthium may also contain tissue from the receptacle. In the apple (a pome), the thickened, fleshy hypanthium is fused with the ovary wall (seed-bearing core). When you eat an apple, you are primarily biting into the hypanthium tissue.
  • Dioecious: A species population containing male plants bearing only male (staminate) flowers and female plants bearing only female (pistillate) flowers. [e.g. cottonwoods (Populus), willows (Salix) and marijuana (Cannabis). This term is incorrectly applied to individual flowers.
  • Monoecious: A species population composed of plants that produce both male (staminate) and female (pistillate) flowers on the same individuals. This term is incorrectly applied to individual flowers.
  • Gynodioecious: A species population containing plants that produce bisexual (perfect) flowers, and plants that produce only female (pistillate) flowers. [In the common edible fig (Ficus carica), the "male" caprifig produces syconia containing unisexual male and female flowers, while the "female" edible fig produces syconia containing only female flowers.]
  • Gynomonoecious: A species population containing plants that produce bisexual (perfect) flowers and female (pistillate) flowers on the same individuals. There are no functional unisexual male (staminate) flowers.
  • Androdioecious: A species population containing plants that produce bisexual flowers and plants that produce only male flowers. [e.g. Certain species of nightshades in the genus Solanum.]
  • Andromonoecious: A species population containing plants that produce bisexual flowers and male (staminate) flowers on the same individuals. There are no functional unisexual female (pistillate) flowers.
  • Polygamous: A species population containing plants that produce bisexual (perfect) and unisexual (imperfect) flowers on the same individual. Not to be confused with human polygamy, or having two or more wives or husbands at the same time. Note: Sometimes the unisexual flowers may contain the rudimentary parts of the opposite sex. [e.g. Toxicodendron diversilobum, better known as poison oak; also species in the Asteraceae with radiate and discoid heads. ]
  • Polygamodioecious: A species population containing plants that are polygamous and plants that are dioecious. [e.g. poison oak.]
  • Polygamomonoecious: A species population containing plants that are polygamous and plants that are monoecious.
  • Complete: Flower with all four characteristic parts present, including the sepals (calyx), petals (corolla), stamens (androecium) and pistil (gynoecium).
  • Incomplete: Flower that is lacking one or more of the four characteristic parts, including the sepals (calyx), petals (corolla), stamens (androecium) and pistil (gynoecium). For example, apetalous flowers are incomplete flowers lacking petals.
  • Perfect: A bisexual flower with functional stamens (androecium) and a functional pistil (gynoecium).
  • Imperfect: A unisexual flower with only one type of functional sex organ. For example, staminate flowers are imperfect flowers that contain only stamens, while pistillate flowers contain only pistils (gynoecia).
  • Chasmogamous: Flowers that open and expose the stamens and styles to cross pollination by wind, water, birds and insects.
  • Cleistogamous: Flowers that do not open and are self pollinated. Cleistogamy insures that a plant produces seeds, even if conditions are unfavorable for wind or insect pollination. Cleistogamy occurs in many different and unrelated plant families, including violets (Violaceae), rushes (Juncaceae) and grasses (Poaceae). Some water lilies (Nymphaeaceae) produce cleistogamous flowers that do not open in rainy weather. The pollen of many angiosperms is damaged by water. In sunny weather, the flowers are open (chasmogamous) and pollinated by insects. There are unconfirmed reports of insect pollinated plants in Timbuctu that produce cleistogamous flowers when the ground temperature is too hot for crawling insects.
  • Viviparous: Seeds and spores that germinate into small plantlets (bulblets) while still attached to the parent plant.
  • Apomixis: Seed development without fertilization. The offspring develop from unfertilized eggs which are often clones of each other. In general there are two main types of apomixis: Parthenogenesis and agamospermy.
  • Parthenogenesis (Agamogenesis): A haploid or diploid egg cell develops into an embryo. Contrary to some authors, parthenogenesis does not always result in genetically identical clones. If the haploid cells are formed by normal meiosis (as in the queen honey bee), crossing over during Prophase I of meiosis may result in some genetic variability. Crossing over is discussed at .
  • Agamospermy: Term applied to an embryo that arises from tissue surrounding the embryo sac. If this involves cells of the nucellus or inner integument it is called a nucellar embryo. Nucellar embryos are chromosomally identical to the sporophyte parent. They are essentially clones of the female parent. Apomictic seeds allow propagation of choice edible fig cultivars (female trees) without the transmission of viruses through cuttings. Mangosteen seeds (Garcinia mangostana) typically contain nucellar embryos and are used to propagate clones of this delicious tropical fruit tree.
  • Parthenocarpic: Term applied to the development of the ovary of a flower into a fruit without fertilization. Fruits that develop parthenocarpically are typically seedless. Some seedless fruits come from sterile triploid plants, with three sets of chromosomes rather than two. The triploid seeds are obtained by crossing a fertile tetrapolid (4n) plant with a diploid (2n) plant. When you buy seedless watermelon seeds, you get two kinds of seeds, one for the fertile diploid plant and one for the sterile triploid. The triploid seeds are larger, and both types of seeds are planted in the same vicinity. Male flowers of the diploid plant provide the pollen which pollinates (but does not fertilize) the sterile triploid plant. The act of pollination induces fruit development without fertilization, thus the triploid watermelon fruits develop parthenocarpically and are seedless. Most bananas purchased at your local supermarket come from sterile triploid hybrids. The fruits develop parthenocarpically and are seedless. Parthenocarpy can be induced by growth hormones such as gibberellic acid (GA3) in which the ovaries mature without fertilization. Grape cultivars such as 'Thompson Seedless' are treated with gibberellic acid to order to produce larger fruits with longer internodes. The bunches have wider spaces between the grapes and better air circulation, reducing their susceptibility to fungal diseases and rotting within the bunch. Contrary to some references, 'Thompson Seedless' grapes are not parthenocarpic because fertilization does occur, but the ovules fail to develop into seeds within the maturing fruit. In cultivated figs, parthenocarpy generally refers to the development of the ovaries of female flowers within the syconium into drupelets without fertilization. The syconium is the structure that you typically associate with an edible fig fruit; however, it is really a flask-shaped inflorescence lined on the inside with numerous unisexual flowers. The actual botanical fruits (called drupelets) develop within the syconium. Since the entire syconium enlarges and ripens into a juicy, sweet morsel, it is often referred to as a fruit. The female flowers are pollinated by a tiny female fig wasp that enters the syconium through a pore called the ostiole. According to W.B. Storey (Advances in Fruit Breeding, 1975), there are 2 genetically determined forms of parthenocarpy: stimulative and vegetative. Stimulative parthenocarpy involves the insertion of the wasp's ovipositor down the stylar canal into the ovary of short style flowers. It can also be induced by blowing air into the syconium, or by spraying the syconium with a plant growth regulator. The mature drupelets may contain a wasp (if an egg was laid in the ovary) or it may be empty. Vegetative parthenocarpy involves the formation of drupelets without any external stimulation, and is responsible for the hollow drupelets inside common figs such as "black mission," "kadota," and "brown turkey." [Some authors use the term parthenocarpy to describe the ripening of seedless fig syconia on the tree without any pollination or fertilization.]
  • Monocarpic: A plant that flowers and bears fruit only once and then dies. Century plants (Agave) and yuccas (Yucca) bloom after 8-10 to 20 years or more and then die.
  • Monocarpous: A gynoecium composed of one carpel.

Strategies For Insuring Cross Pollination:

1.   Cross Pollination: The transfer of pollen from the anthers of Plant A to the stigmas of Plant B. [Self pollination is the transfer of pollen from the anthers of Plant A to the stigmas of Plant A.] Cross pollination provides greater genetic variation, the raw material for evolution.

2.   Dioecious Species: Populations with separate male (pollen-bearing) and female (seed-bearing) plants must be cross pollinated. Approximately 3-4 percent of all flowering plants are dioecious. Although dioecism favors cross pollination, there is reduced seed production because only half of the population (the female plants) bear seeds.

3.   Maturation Sequence Of Anthers & Stigma: The pollen-bearing anthers and receptive stigmas in the flowers of a given plant mature at different times. Therefore, pollination must occur between the anthers and stigmas of different individuals within the population that have the same maturation sequence.

§         Protogynous Flowers: The stigma is receptive before the anther releases pollen. [e.g. Plantains, magnolia, avocado, figs (Ficus) and wolffia.]

§         Protandrous Flowers: The stamens mature and release pollen before the stigma is receptive. [e.g. Sunflower, cornflower, sage (Salvia) and verbena.]

4.   Heterostyly: A population containing plants with flowers containing high anthers & low styles, and plants with flowers containing high styles and low anthers. Cross pollination is favored when pollen is transferred from high anther flowers to high style flowers. [e.g. primose (Primula).

5.   Thigmotrophic Stigma: The two-lobed stigma of red bush monkeyflower (Mimulus puniceus) is sensitive to touch and rapidly closes if touched by your finger or the bill of an incoming pollinator. This action decreases the chance of self pollination and favors cross pollination. When the bill or head of a hummingbird enters the blossom and touches the stigma it immediately closes. Pollen carried by the bird is trapped within the closed stigma lobes. As the bird probes for nectar deep in the corolla it also picks up fresh pollen from the anthers. But when it leaves, there is little chance of this newly acquired pollen touching the stigma because it is already closed, thus averting any self pollination.

6.   Self-Incompatible Pollen: In the androdioecious flowers of certain nightshades (Solanum), the pollen in plants with bisexual flowers is sterile. This infertile (inaperturate) pollen does not have apertures when viewed under a microscope and is non-stainable. Without fertile pollen, the bisexual flowers are functionally female. Male plants in the population with functional staminate flowers produce viable pollen which cross pollinates with the "female" plants.

7.   Flynapping Arums & Dutchman's Pipe: The arum family (Araceae) is characterized by a phallus-like inflorescence called a spadix bearing clusters of protogynous, pistillate flowers below the staminate flowers. The spadix is often enveloped by a colorful, funnel-like spathe. A truly remarkable arum (Helicodiceros muscivorus) with an ingenious fly trap is native to the rocky Mediterranean islands of Sardinia and Corsica. With a stench reportedly as strong as a sheep carcass, blow flies are lured into a pitch dark, fetid chamber at the base of the funnel-like spathe. Carrying pollen from another plant, they inadvertently pollinate the receptive female flowers at the base of the chamber. Unable to escape from the chamber due to a dense rosette of stiff hairs, the flies remain prisoners until the male flowers above the stiff hairs start to release pollen. Then the barricade of hairs wilts and the flies are able to escape, getting dusted with pollen as they leave the damp and putrid-smelling chamber. The European Dutchman's pipe (Aristolochia clematitis), a member of the birthwort family (Aristolochiaceae), has a similar ingenious method of incarcerating insects until its male flowers shed pollen.

8.     Contact Pollination: This method of pollination involves the male and female flowers of dioecious species (e.g. Vallisneria) and the male and female organs of bisexual, protogynous species (e.g. duckweeds of the Lemnaceae). The male flowers of Vallisneria and the pollen-bearing plant bodies of bisexual duckweeds (e.g. Lemna and Wolffia) are pushed along the water surface where they bump into receptive female flowers of Vallisneria and the gynoecia of bisexual duckweeds.