Erasanthe henrici (Schltr.), 2007

Cribb, Phillip J., Hermans, Johan & Roberts, David L., 2007, Erasanthe (Orchidaceae, Epidendroideae, Vandeae, Aerangidinae), a new endemic orchid genus from Madagascar, Adansonia (3) 29 (1), pp. 27-30 : 30

Erasanthe henrici (Schltr.)

P.J.Cribb, Hermans & D.L.Roberts subsp. isaloensis H.Perrier ex P.J.Cribb, Hermans & D.L.Roberts , subsp. nov.

Aeranthes henrici Schltr. var. isaloensis H.Perrier, Flore de Madagascar, Orchidées 2: 138 (1941), nomen nudum.

A subspecie typica bracteis triangularibus acutis, floribus minoribus, lamina tranverse elliptica et columna longiore differt.

TYPUS. — Madagascar. Isalo , X.1924 , H. Perrier de la Bâthie 16895 (holo-, P!).

REMARKS

The sole species E. henrici is represented by two subspecies: the typical one is found north of Antananarivo to Tsaratanana Madagascar whereas subsp. isaloensis is confined to gorges in the Isalo Massif and remnant forests to the south-west towards Toliara.It differs from the typical subspecies in its triangular, acute floral bracts and smaller flowers which have a lip with an elliptic-transversal basal lamina extending into a square blade and a shorter acuminate apex, a shorter spur, shorter pedicel and ovary, and a column that is longer and distinct in structure.

The typical subspecies is found in the humid forests of the plateau to the north and north-east at between 800 and 1000 m. These are disappearing as the land is cleared for agriculture or through accidental forest fires when the surrounding grassland is burnt by a rapidly increasing population. Subspecies isaloensis grows low down on the trunks and branches of trees near water-courses in the deep canyons of the sandstone Isalo Massif and also further west on small trees and shrubs at 750 m in the Sakaraha-Zombitsy dry forest, the latter being rather badly burnt and logged especially in easily accessible areas. More recently the subspecies was found during a brief expedition to the unusual wet forest fragment on Analavelona.

Erasanthe henrici is one of the most beautiful of Madagascan orchids although difficult to flower in cultivation, as a result it has been widely overcollected from the forest remnants. At one location over 1000 individuals of the subspecies isaloensis were stripped in 1993, more than 10 years later the population has failed to recover. Such overcollecting of both subspecies still continues. Due to habitat destruction and over-collecting, both subspecies are considered to be threatened with extinction ( henrici VU D 2; isaloensis EN B1ab (iii, v) B2ab (iii, v)) ( IUCN 2001). However, efforts are underway in Madagascar to produce a supply for the horticultural industry using micro-propagation techniques which should reduce the necessity of further collection from the wild.