Didymeles is a genus of flowering plants. It is variously treated as the only genus of the family Didymelaceae — or in the family Buxaceae, as in the APG IV system.
The genus Didymeles is restricted to Madagascar and the Comoros. In Madagascar, the two species are found in humid montane habitats, up to 1,500 m, in two disconnected areas in the north-east and south-east of the island.[1] Fossils assignable to this genus have been found in New Zealand,[2] suggesting a much wider distribution in the past.
Species are dioecious (i.e. "male" and "female" flowers occur on separate plants). Individual flowers have a very simple structure, without obvious petals or sepals. Female flowers have been interpreted in different ways, either as having two carpels or as occurring close together in pairs, each with a single carpel.
Didymeles species are evergreen trees. The simple leaves are leathery in texture, with untoothed (entire) margins. There are no stipules. The flowers are unisexual, with the two kinds borne on separate plants (i.e. the species are dioecious). The staminate ("male") flowers are arranged in short panicles. Each flower basically consists only of two stamens.[3] The carpellate ("female") flowers are arranged in thyrses (spike-like structures). At the base of the inflorescence there are a number of empty bracts followed by up to 15 bracts arranged in a spiral, each of which is at the base of a side branch of the inflorescence. At the apex of each side branch there is a structure made up of two larger "scales", each with a smaller "scale" at its base, and two carpels, somewhat separated from one another, often with a small "hump" in between.[4] The pollen of Didymeles is distinctive. The grain has three furrows (colpi), as is commonly the case for eudicots; but each colpus then contains two circular openings or pores.[3]
The carpellate flowers have been interpreted differently. When the genus was first described, the two carpels were considered to belong to a single flower, each "female" flower having two carpels just as the "male" flowers had two stamens. This interpretation has been accepted by some later researchers. The "scales" then correspond to tepals of the single flower. The alternative interpretation, preferred by von Balthazar et al., is that there are two flowers very close together, each with a single carpel. Only the smaller "scale" might then correspond to a tepal.[4]
Each carpel has a broad two-crested stigma on a short style, and usually contains a single ovule. The integument – the covering on the outside of the ovule – is in the form of a long coiled tube, an unusual feature in flowering plants. The fruit which forms after fertilization is a fleshy drupe, to which the stigma remains attached.[4]