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Published In: Flora Indica; or descriptions of Indian Plants 2: 148. 1824. (Fl. Ind.) Name publication detailView in Biodiversity Heritage Library

Project Name Data (Last Modified On 10/19/2010)
Acceptance : Accepted
Taxon Profile     (Last Modified On 7/21/2011)
Generic Distribution: not endemic to the Malagasy Region
Generic Species Diversity and Endemism Status: has been evaluated
No. of species in Fl. Madagasc.: not published
Accepted Published Species: 13 endemic
Estimated Unpublished Species: none
Estimated Total Species: 13 endemic
Additional Taxonomic Work: not currently required
Species Level Data Entry: complete

Hymenodictyon is closely related to Paracorynanthe; these genera share a woody, sometimes deciduous habit; interpetiolar, triangular, often deciduous stipules; cymose, bracteate inflorescences that are terminal and often also produced in the uppermost leaf axils; bisexual flowers with 5 calyx lobes, corolla lobes, and stamens; funnelform corollas with the lobes valvate in bud; rather small, ellipsoid, lenticellate, capsular fruits with loculicidal dehiscence; and one to numerous flattened, winged seeds per locule. Some species in both genera characteristically have a pair of petaloid, long-stipitate bracts borne at the base of the inflorescence. These are generally pale green to white or sometimes pink. Razafimandimbison & Bremer (2006) revised these genera, and found them together to comprise the tribe Hymenodictyeae which is closely related to Naucleeae.

See Paracorynanthe for a key to these genera. Paracorynanthe differs from Hymenodictyon as well as the other Rubiaceae in Madagascar in its unusual corollas, which have each lobe ornamented at the tip by a prolonged appendage that comprises a pilose stipe 3-4 mm long that bears a black globose club. The inflorescences of Paracorynanthe are rounded or corymbiform in general shape, while in Hymenodictyon the inflorescences or at least the axes are often spiciform. The ovaries of Paracorynanthe have 1-2 ovules per locule, while those of Hymenodictyon have 2-40 ovules per locule. The bark of Paracorynanthe characteristically falls in large plates or plaques while the bark of Hymenodictyon is generally not divided into plates.

Razafimandimison & Bremer (2006) presented a mostly natural key to the species of Hymenodictyon; an alternative key is presented here based on the species circumscription of Razafimandimbison & Bremer, but incorporating more recently collected specimens. Identification of Hymenodictyon species in our region is complicated by the deciduous phenology of the plants, with the inflorescences often produced together with the young leaves, the leaves maturing when the fruits are young, and then the leaves falling off plants with mature infructescence. Thus matching plants at different developmental stages can be complicated. Razafimandimbison & Bremer separated species in part by whether the inflorescences are branched or simple; in these species sometimes only the terminal inflorescence is branched while the several inflorescences borne in the uppermost leaf axils are simple, also this character can sometimes be difficult to discern on older infructescences where some axes have fallen off. In many if not most species of Hymenodictyon in our region, the inflorescences are rather compact with the flower grouped closely together but the primary axis elongates, sometimes markedly, as the fruits develop so the size of the mature infructescence is sometimes quite different. The soft, white or colored petaloid bracts appear to function to attract pollinators in the inflorescences, but in many species these then become stiffened and are persistent on the infructescences also, where their function is not yet known. Some petioles measurements were given incorrectly by Razafimandimbison & Bremer as mm rather than cm.

Compiled or updated by: S. Andriambololonera & S. Andrianarivelo; notes and key added by C.M. Taylor VII 2011

Images and Maps     (Last Modified On 7/21/2011)
Maps: Distribution maps: Razafimandimbison & Bremer, 2006: p. 341, fig. 3; p. 344, fig. 5; p. 347, fig. 7; p. 353, fig. 9.




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