Papilionaceous flower

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Wisteria sinensis anatomia rev en.svg
Flower parts of a Chinese wisteria. It has a diadelphous stamen morphology (one stamen not fused with the remaining nine), which Linnaeus classed as the Diadelphia.
Sesbanea bispinosa, crop.jpg
Dissected flower parts of Sesbania bispinosa

Papilionaceous flowers (from Latin: papilion, a butterfly) are flowers with the characteristic irregular and butterfly-like corolla found in many, though not all, plants of the species-rich Faboideae subfamily of legumes. Tournefort suggested that the term Flores papilionacei originated with Valerius Cordus, [1] who applied it to the flowers of the bean. [2]

Contents

Structure

Corolla

The flowers have a bilateral symmetry with the corolla consisting of five petals. A single, large, upper petal is known as the banner (also vexillum or standard petal). The semi-cylindrical base of the banner embraces and compresses two equal and smaller lateral wings (or alae). The wings in turn enclose a pair of small keel petals, that are situated somewhat lower than the wings, but are interior to them. [1] They have concave sides and correspond with the shape of the wings. The two keel petals are fused at their bases [3] or stuck together [4] to form a boat-shaped structure that encloses the essential flower organs, [5] namely the androecium and gynoecium. Typically these flowers have a vexillary (i.e. descendingly imbricate or overlapping) aestivation. [3]

Stamens

The stamens often have a diadelphous morphology, meaning that they are united in two sets with a distinct filament shape in each set. [1] The inferior set forms a membranous sheath at its base, that envelops the single, superior pistil in a tube. The tube divides into nine filaments, which trace the base of the keel petals that enclose them. [1] The single free filament lies above them. In Smithia the two sets are equal, with 5 stamens in each. [1]

Many papilionaceous flowers however have ten distinct stamens. Genera that conform to the latter morphology include Sophora , Anagyris , Cercis , Daviesia , Dillwynia , Gompholobium , Mirbelia and Pultenaea . [1]

Ecology

A bee pollinating the flower of Bossiaea cinerea. Bee bossiaea cinerea cropped.jpg
A bee pollinating the flower of Bossiaea cinerea .

Charles Darwin observed that the fertility of plants with papilionaceous flowers depend to an important extent on visits by bees, [6] and it is accepted that this corolla structure evolved under selective pressure of bee pollinators. [7] Linnaeus remarked that they produce hardly any scent, but the flowers of Spanish broom, sweet pea, scorpion vetch, European yellow lupine, fava bean and various species of clover are notable exceptions. [1]

Four different mechanisms of pollen release are known in papilionaceous flowers, which are respectively known as the explosive, valvular, piston and brush mechanisms. [7] In the explosive or tripping mechanism (cf. alfalfa, common broom, ox-eye bean [8] ) all pollen is instantly released when pressure on the staminal column is permanently released (usually by an insect) causing it to snap against the standard petal. In the valvular mechanism pollen is released repeatedly when pollinators unseal the upper rim of the keel petals, and force them downwards. In the piston mechanism (cf. scorpion senna [7] ) pollen is released repeatedly when the keel tip is moved by an insect so as to release pollen through a hole in the tip. The brush mechanism employs a pistil which is longer than the stamens, so as to avoid self-pollination. When a pollinator presses against the standard and wing petals, a brush on the temporarily lifted pistil brushes pollen onto the pollinator, while the stigma receives external pollen. [7]

Examples and exceptions

Well-known plant genera in the Faboideae which exhibit this corolla morphology include beans, peas, sweet peas, alfalfa (lucerne), clovers, lupines, smoke trees, black locusts, locoweeds and coral trees. [9] [10] The flowers of coral trees are diadelphous and are considered papilionaceous, but the wings are much reduced, suggesting a flower with three petals. [1] [10] Their keel petals are elongate, fused together and sometimes tubular to facilitate pollination by certain bird groups, [10] while secondary compounds in their nectar seem to repel bees. [11]

The false indigo genus, though belonging to the Faboideae, does not exhibit a papilionaceous corolla morphology, as it has only one petal per flower, [12] namely the banner. [1] [3] The corolla of clovers tends to be monopetalous, as all five petals are often fused below to form a tube. [1]

Other legume subfamilies

To the contrary, plants in the Mimosoideae subfamily of legumes have the petals reduced, and have numerous stamens arranged in showy spikes. In the Caesalpinioideae subfamily of legumes the upper petal is initially enveloped by the lateral petals, before the petals unfold to assume a radial five-fold symmetry. [9] The aestivation of Mimosoideae, Caesalpinioideae and Faboideae is presented in diagram below.

Aestivation in Mimosoideae Caesalpinioideae Faboideae.svg

See also

Related Research Articles

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The Fabaceae or Leguminosae, commonly known as the legume, pea, or bean family, are a large and agriculturally important family of flowering plants. It includes trees, shrubs, and perennial or annual herbaceous plants, which are easily recognized by their fruit (legume) and their compound, stipulate leaves. The family is widely distributed, and is the third-largest land plant family in number of species, behind only the Orchidaceae and Asteraceae, with about 765 genera and nearly 20,000 known species.

<span class="mw-page-title-main">Petal</span> Part of most types of flower

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<span class="mw-page-title-main">Stamen</span> Male organs of a flower

The stamen is a part consisting of the male reproductive organs of a flower. Collectively, the stamens form the androecium.

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<i>Sesbania punicea</i> Species of legume

Sesbania punicea is an ornamental shrub with reddish-orange flowers native to South America. It has deciduous leaves and grows to a height of 15 feet. This plant has a high demand for water, and thrives in swamps or wet areas. It requires a mildly acidic soil, with a pH between 6.1 and 6.5.

Otholobium dreweae is an upright shrublet assigned to the Pea family of about 15 cm (5.9 in) high, that appears after the vegetation burned down from the underground rootstock and forms mat-like clumps of hardly branching, leafy stems. The stems are set with stiff, entire, alternate leaves with a single leaflet and heads consisting of 12-18 initially dark pink, later white, pea-like flowers with a white nectar guide on a peduncle as long as the leaves at the end of the stem. This species is an endemic of the Kleinrivier Mountains in the Western Cape province of South Africa. It mostly flowers in November.

Otholobium accrescens is an upright, largely herbaceous subshrub assigned to the Pea family. It has up to three stems that carry upright branches in leaf axils near the ground, and have alternately set inverted egg-shaped leaves and lax heads consisting of 12-21 pea-like flowers on long peduncles in the axils of the lower leaves. It differs from most other Otholobium species by the calyx that continues to grow after flowering and the leaf that consists of just one leaflet. It is an endemic of the Eastern Cape province of South Africa near Loerie. It probably flowers August to January.

<i>Otholobium nitens</i> Shrub in the family Fabaceae from South Africa

Otholobium nitens is an upright, densely branched shrub of up to 1.5 m high that is assigned to the Pea family. It has one to many initially softly hairy stems, alternately set, clover-like, upright leaves crowding the new shoots, and heads consisting of 3 pea-like, dark purple to mauve flowers on short peduncles in the axils of the leaves on short side-shoots. This species is an endemic of the mountains between Ceres and Hottentots Holland in the Western Cape province of South Africa. It mostly flowers between October and late December.

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<i>Otholobium spissum</i> Shrub in the family Fabaceae from South Africa

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<i>Otholobium lucens</i> Shrublet in the family Fabaceae from South Africa

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References

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  2. ↑ Cordus, Valerius (1561). "162". Historia Stirpium et Sylva.
  3. 1 2 3 Reddy, S. M. (2007). University Botany III: (Plant Taxonomy, Plant Embryology, Plant Physiology). Vol. 3. New Age International. pp. 60–64. ISBN   9788122415476.
  4. ↑ "Botanical term: papilionaceous". nswildflora.ca. Nova Scotia Wild Flora Society. 2007. Archived from the original on 4 March 2016. Retrieved 24 March 2015.
  5. ↑ Gupta, P.K. (2007). Genetics: classical to modern (1 ed.). Meerut, India: Rastogi Publications. pp. 146–147. ISBN   978-8171338962.
  6. ↑ Darwin, Charles (2007). "IV: On the advantage". On the origin of species by means of natural selection, or, The preservation of favored races in the struggle for life. New York: Cosimo Classics. p. 62. ISBN   978-1602061446.
  7. 1 2 3 4 Aronne, Giovanna; Giovanetti, Manuela; De Micco, Veronica (2012). "Morphofunctional Traits and Pollination Mechanisms of Coronilla emerus L. Flowers (Fabaceae)". The Scientific World Journal. 2012: 381575. doi: 10.1100/2012/381575 . PMC   3361249 . PMID   22666114.
  8. ↑ Mosquin, Ted. "The explosive pollination mechanism in Cornus canadensis L." Botanical Electronic News. The Canadian Field-Naturalist, Volume 99, Number I, Jan.-Mar. 1985. Retrieved 25 March 2015.
  9. 1 2 Armstrong, W. P. "Flower Terminology Part 2, 14. Flower Definitions". Wayne's Word, Botany 115 Terminology. Archived from the original on 20 March 2015. Retrieved 25 March 2015.
  10. 1 2 3 Armstrong, W. P. "1. Family Fabaceae - Subfamily Papilionoideae". Wayne's Word, Botany 115 Terminology. Archived from the original on 9 March 2015. Retrieved 25 March 2015.
  11. ↑ Nicolson, Susan W.; Lerch-Henning, Sara; Welsford, Megan; Johnson, Steven D. (16 May 2015). "Nectar palatability can selectively filter bird and insect visitors to coral tree flowers". Evolutionary Ecology. 29 (3): 405–417. doi:10.1007/s10682-014-9718-7. hdl: 2263/51251 . S2CID   254468205 . Retrieved 1 July 2016.
  12. ↑ Wooten, Robert K. Godfrey; Jean, W. (1981). Aquatic and wetland plants of southeastern United States: Dicotyledons. Athens, Ga.: University of Georgia Press. p. 236. ISBN   0820342432.{{cite book}}: CS1 maint: multiple names: authors list (link)
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