Haptanthus
Haptanthus is a monotypic genus containing the sole species Haptanthus hazlettii, a shrub or small tree known only from the locality of Matarras in the Arizona Municipality in Honduras. Its flowers are unique among the flowering plants. A single "female" (carpellate) flower has two branches on either side which carry "male" (staminate) flowers. The flowers are very simple, lacking obvious sepals or petals. The family placement of the genus has been uncertain, but based on molecular phylogenetic research, it is included in the family Buxaceae as of September 2014[update].[3] Very few individuals have ever been found and its habitat is threatened by logging.
Haptanthus hazlettii is a shrub[4] or tree.[3] It has opposite leaves spaced at 5.5–6.0 cm apart, usually arranged in two ranks (distichous). The leaves are simple with untoothed (entire) margins. There are no stipules. The leaf stalk (petiole) is short, 7–8 mm long, the leaf blade (lamina) 10–13.5 cm long by 4.1–5.6 cm wide. The entire plant is hairless (glabrous).[4]
The flowers are unisexual, carried on the same inflorescence (i.e. the plant is monoecious). One (or occasionally two) inflorescences emerge from a leaf axil, with at least five inflorescence-bearing axils per fertile branch. The inflorescences have a unique structure among flowering plants. In the centre there is a single carpellate ("female") flower. This lacks obvious petals or sepals (although there are small bracts below the flower which some researchers have suggested may be the remnants of the perianth[5]), and consists solely of a single-celled (unilocular) ovary, 5 mm long by 2 mm wide, surmounted by three curved 4 mm long stigmas. On either side of the solitary carpellate flower there are two branches each with five or six staminate ("male") flowers arranged at 1–3 mm intervals.[4]
The structure of the staminate flowers has been interpreted differently. The original describers of the species, Aaron Goldberg and Cirilo Nelson, considered that each staminate flower was basically just a single stamen, with a flattened filament about 3–5 mm long grading into an anther about 2.5 mm long.[4] Two staminate flowers from the original specimen were re-examined by Andrew Doust and Peter Stevens. They concluded that each staminate flower definitely had two anthers, closely pressed together. They were unable to make a firm choice between two interpretations. The first is that the staminate flowers are basically as described by Goldberg and Nelson, except there are two stamens with fused or closely pressed filaments and anthers rather than one. The second, which they preferred, is that Goldberg and Nelson's "filament" is actually a pedicel (i.e. a stem on which the parts of the flower are carried) and that their "anther" consists of two closely pressed structures each made up of a tepal with a fused anther inside it. Either way, the flowers of Haptanthus hazlettii have "a morphology unlike that of any other angiosperm".[5]
