7. Ayenia Linnaeus, Kongl. Svenska Vetensk. Acad. Handl. 17: 23, plate 2. 1756.
[For Louis de Noailles, 1713–1793, first Duc d’Ayen] [For Louis de Noailles, 1713–1793, first Duc d’Ayen]
Laurence J. Dorr
Nephropetalum B. L. Robinson & Greenman
Subshrubs or shrubs [trees], erect, ascending, or decumbent; taprooted. Stems unarmed, hairy 3–7-veined from base. Inflorescences axillary or terminal, cymose, 1–11-flowered; epicalyx absent. Flowers bisexual [rarely unisexual or cleistogamous]; sepals basally connate, basally abaxially glandular-hairy; petals clawed, claws filiform, lamina rhombic, deltate, reniform, or ± triangular, base divided into 2 lobes or not, lobe margins entire or erose, apex notched, entire, or with 2 widely spaced teeth, surfaces glabrous or hairy, abaxial surface appendaged or not, appendage ± filiform, cylindric, or clavate, inserted in middle of lamina distally, petals inflexed toward center of flower and connivent to apex of staminal tube such that when viewed from above corolla resembles a disc with staminodes, style, and stigma, if exserted, protruding from center; androgynophore present [absent]; staminodes 5, connate into cylindric or ± rounded, minute or indistinct. Fruits capsules, often pendulous, oblate or subspheric, 5-locular, dehiscence septicidal and then loculicidal, hairy [glabrous], prickled. Seeds 1 per locule, ovoid, smooth, wrinkled, or tuberculate; endosperm absent; cotyledons leafy, folded and rolled around hypocotylar axis. x = 10.
Species ca. 80 (7 in the flora): United States, Mexico, West Indies, Central America, South America (to Argentina and Paraguay).
The name Ayenia pusilla Linnaeus has been misapplied to some species found in the flora area. C. L. Cristóbal (1960) selected the South American element in the Linnaean protologue of this name as lectotype; the name is now correctly applied only to a species in Ecuador and Peru.
Molecular data (B. A. Whitlock and A. M. Hale 2011) indicate that a monophyletic Ayenia is embedded within a paraphyletic Byttneria Loefling and that the monospecific, Brazilian endemic Rayleya Cristóbal is sister to a combined clade of Ayenia and Byttneria. The taxonomic implications of these relationships have not been fully resolved. A relatively small proportion of species in this Ayenia/Byttneria/Rayleya clade have been sampled and the African genus Megatritheca Cristóbal, which shows a combination of morphological features usually associated with either Ayenia or Byttneria, has not been included in molecular analyses.
The structure of Ayenia flowers is complicated and the terminology applied to the various parts has not been consistent (see L. J. Dorr 1996 and included references). In particular, the terms claw and lamina as applied to petals have been used to describe different structures. termed a gland or ligule) or not. W. Leinfellner (1960), using comparative and developmental data, argued that the rhombic, deltate, or reniform portion of the petal (lamina) is homologous with the distal part of the claw and that the lamina is reduced to an appendage or absent.
SELECTED REFERENCES Cristóbal, C. L. 1960. Revisión del género Ayenia (Sterculiaceae). Opera Lilloana 4: 1–230. Whitlock, B. A. and A. M. Hale. 2011. The phylogeny of Ayenia, Byttneria, and Rayleya (Malvaceae s.l.) and its implications for the evolution of growth forms. Syst. Bot. 36: 129–136.