Brexia Madagascariensis

''Brexia'' is a plant genus assigned to the Celastraceae. It is a dense evergreen shrub or small tree of usually around 5  m high, with alternately set, simple, leathery leaves with a short leaf stem and lanceolate to inverted egg-shaped leaf blades. The pentamerous flowers occur in cymes. The petals are greenish white, the samens are alternating with wide, incised staminodes. The superior ovary develops in a long ribbed fruit. ''Brexia'' naturally grows on the coast of East Africa, on Madagascar, the Comoros and Seychelles. Opinions differ about the number of species in ''Brexia''. Sometimes the genus is regarded monotypic, ''B. madagascariensis'' being a species with a large variability, but other authors distinguish as many as twelve species. Common names for ''B. madagascariensis'' include jobiapototra, tsimiranjana, tsivavena, vahilava, voalava, voankatanana, voantalanina, voatalanina and votalanina (all Malagasy), and mfukufuku ( Swahili), mfurugudu ( Shambala, Tanzania) and bwa kato (Seychelles). cited on

Description

Stems and leaves

''Brexia'' is a shrub or small tree, usually 3–7, but occasionally up to 10 m high with many branches, that are smooth with ridges early on but later becoming cylindrical. The leaves are evergreen, with a leaf stem mostly 1–2 cm long, but sometimes very short. The leathery leaf blades are between 3½ and 50 cm long and 2 and 11 cm wide, with large differences in shape, narrowly inverted egg-shaped to linear with teeth or even spines along the edges in young growth, while on mature shoots they may be narrowly to broadly inverted egg-shaped and the edge toothy to entire, with a rounded to indented tip, and wedged along the leaf stem or rounded at the base. The stipules are very narrow.

Flowers

Each inflorescence may consist of usually between three and twelve flowers, but may occasionally contain as few as one and as many as seventeen flowers, usually on a flattened 1½−5 mm wide common stem of up to 9 cm long, and growing from a leaf axil, but in some forms on thick branches or the trunk (so-called cauliflory). Sometimes near the tip are one or two persistent leaf-like bracteoles of about 1 cm, but mostly the small scale-like bracteoles fall off quickly. Individual flowers are on stems of up to 2 mm long. Each flower has five sepals of about 2½ × 3½–4 mm, the lower half of which are fused, the free tips short triangular with a rounded tip and an entire edge. The five fleshy petals are greenish or creamy white, 1¼–1¾ × ⅞–1¼ cm, broadly inverted egg-shaped, with a blunt tip. The five stamens have filaments of about 1¼ mm thick, and are topped by anthers of 5 × 2½ mm. Alternating with the stamens are mostly unequally incised staminodes with three to five incisions. The superior ovary has five sides and is 8–10 mm high including the style.

Fruit and seed

The fully grown fruit is a drupe of 4–10 × 2–3 cm, ovoid to cylindric, with five prominent ribs, with the mesocarp initially woody but supposedly pulpy and edible when fully ripe. It contains brown or almost black, finely wrinkled, irregularly compressed, oval, keeled seeds of 4½–7½ × 3–3½ mm. ''cited on''

Differences with other genera

''Brexia'' has been assumed to be closely related to Escallonia. These two genera however differ in many details of the sporogenesis, gametogenesis and fertilisation, such as the ripe pollen which is two-celled in ''Escallonia'' and three-celled in ''Brexia''.

Taxonomy

''Brexia'' is a deviant genus, that was assigned early on to the Brexiaceae or Brexioideae, together with two other enigmatic, monotypic genera, ''Ixerba'' and ''Roussea''. The common characters between these taxa are few and are shared with many other Pentapetalae. These common characters include that they are all small trees or shrubs with simple leathery evergreen leaves, with an entire or serrated margin, and pentamerous flowers set individually or in cymes in the axil of the leaves. Botanist have differed on the rank and placement of these three genera. They have by some authors also been assigned to the Escalloniaceae, Saxifragaceae, Grossulariaceae, and the Hydrangeaceae. Genetic data indicate that the three genera are not each other's closest relatives, in fact are not closely related at all. ''Ixerba'' has now been included in the Strasburgeriaceae. ''Roussea'' is most related to ''Carpodetus'', ''Cuttsia'' and ''Abrophyllum'', that are nowadays combined in the family Rousseaceae, the sister group of the Campanulaceae, and together representing the basic branche of the Asterales. ''Brexia'' is closely related to the large celastracean genera ''Pleurostylia'' and ''Elaeodendron