Alsophila borbonica, synonym Cyathea borbonica, is a tree fern endemic to Mauritius and Réunion. There are several natural forms and varieties.
Description
It reaches a height of roughly 2 meters, with a dark, hairy, scaly trunk. Its spreading leaves are dark green fronds. Each frond has a relatively small stem (stipe). Each leaf also divides only twice (bipinnate): The central midrib of the frond (rachis) branches into many horizontal leaflets (pinnae). Each pinna midrib bears many small leaflets (pinnules).
Forms and distribution There are two natural Mauritian varieties, which occur mainly in the upland forest in the higher parts of the island, and are both endangered. There is one natural Reunionese variety:
A. borbonica var. borbonica (Réunion) A. borbonica var. latifolia (Mauritius), which bears an umbrella-shaped crown A. borbonica var. sevathiana (Mauritius), which bears a funnel-shaped crown
Related species In Mauritius, they share the island with several other tree ferns - the naturally occurring Mauritian species Alsophila grangaudiana and Alsophila celsa - and the alien non-indigenous Sphaeropteris cooperi which is introduced from its native Australia.
In Réunion, they share the island with the naturally occurring Réunionese species Alsophila glaucifolia and Alsophila celsa - and also with the introduced Sphaeropteris cooperi.A revision of the fern family Cyatheaceae in the Mascarene Islands (2006)
Alsophila borbonica can be distinguished from all of these other species by its small stipe and by its fronds' two-level division.M. Glaubrecht (2010): Evolution in Action: Case studies in Adaptive Radiation, Speciation and the Origin of Biodiversity. Springer Science & Business Media. Science. p.13.
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