Megistostegium perrieri Hochr.

Koopman, Margaret M., 2011, A synopsis of the Malagasy endemic genus Megistostegium Hochr. (Hibisceae, Malvaceae), Adansonia (3) 33 (1), pp. 101-113 : 112

Megistostegium perrieri Hochr.

Annuaire du Conservatoire et du Jardin botanique de Genève 18-19: 225-226 (1915). — Holotype: Madagascar, Toliara, Sud-Ouest: dunes et calcaire-Plateau Mahafaly (Menarandra), VI.1910, Perrier de la Bâthie 5470 (= Hochreutiner 15) ( G).

ADDITIONAL MATERIAL EXAMINED. — Madagascar. Prov. Plateau calcaire, Lavanono (sud), 2.III.1967, J . Bosser 19076 ( MO). — Sud-ouest: environs du Cap Ste Marie, 29.III.1959, R . Capuron 11861- SF ( P) . — Along bluffs overlooking Indian Ocean, c. 5 km NE of Lavanono, alt. 150 m, 17.II.1975, T . B . Croat 31539 ( MO). — Beharambolo, calcaire d’extrême sud, 2.VIII.1922, R . Decary s.n. ( P). — Sud, Cap Ste Marie, 20. I .1961, B . Descoings 2539 ( MO). — Cap Ste Marie, Marovato, Tsiombe, terroir sec, 11. VI .1948, Ratoto Jean de Dieu 1430 ( P). — Cap Ste Marie Reserve, SW of Tsiombe, 25°35’S, 45°09’E, alt. 200 m, 28.XII.1992, P . B . Phillipson 3003 ( MO). — Préfecture de Tôlanaro (Fort Dauphin), 25°57’S, 45°15’E, 27. I .1994, R . Rabevohitra 2215 ( MO). — Beloha, Cap Ste Marie, 25°35’S, 45°08’E, alt. 181 m, 25.XI.2006, R . Ranaivojaona 534 ( MO). — Cap Ste Marie Special Reserve, 300 m W of lighthouse, 25°35’S, 45°07’E, alt. 190 m, 18.II.1990, G . E . Schatz 2971 ( MO) .

DESCRIPTION

Sturdy, prostrate subshrubs (1-10 dm tall; Fig. 1 ). Leaves large(1.8-5.4 × 1.3-3.4 cm), thick(1.2-5 mm), succulent, covered with soft, tomentose white stellate trichomes and interdispersed with rare, stiff, yellow hairs gray-green, orbicular to rotund (apex often with a rounded mucron), localized at branch tips (due to extreme internode compression). Stipules foliaceous, filiform to lanceolate, persistent with leaves usually equal in length to the petioles. Flowers pendant, often hanging centimeters from the ground.Epicalyx campanulate, sharp acuminate tips, deep maroon in color when mature and covered in stellate hairs. Corolla forms wide cup, 1.2 cm at the rim. Staminal column stout, exserted 0-2.7 cm past the corolla. Pollen yellow and sticky when fresh, average diameter of grain 124 µm with numerous (about 110) long, cylindrical echinae (11 µm tall × 3.8 µm wide at base) and approximately 148 large (3.4 µm wide) apertures.

DISTRIBUTION AND ECOLOGY

Megistostegium perrieri is restricted to the windswept calcareous coastlines of the Mahafaly plateau (Tertiary limestone) at Cap Sainte Marie (Tanjona Vohimena) and Lavanono ( Fig. 2). The short stature of this plant is likely partly in response to the constant wind blowing off the Mozambique Channel. When plants are found in sheltered, rocky outcoves on cliffs, plants can grow taller. These plants grow in an average of 4.27 cm (± 2.44) of soil but can persist on bare rock. Megistostegium perrieri flowers from late December through late March (with single flowering herbarium collections in November and June).

REMARKS

Ethnobotany

Megistostegium perrieri is the most under-utilized species in the genus, probably due to its remote and restricted distribution. A leaf decoction is used as a cough suppressant, and flowering boughs are used ornamentally (pers. obs.).

Vernacular names

Tsomontsoy vavy, Tsomontsoy, Sognogne.

CONSERVATION STATUS

Megistostegium perrieri is restricted to the Special Reserve of Cap Sainte Marie (a protected area that remains threatened by invasive plants and animals) and adjacent Lavanono (unprotected).After extensive searches over two field seasons, no pollinator has been observed visiting this taxon.Results from comparisons between experimental crosses and natural seed set indicate that M. perrieri is pollen-limited in the field (Koopman 2008). Extensive pollination observations (diurnal and nocturnal) over several field seasons indicate that the pollinator of M. perrieri may be extinct. If care is not taken to protect these unique calcareous plateaus, this species will no doubt be lost. The limited distribution of the species (EOO: 300 km 2 and AOO: 70 km 2) to only two known locations, and with assured continuing decline at the unprotected Lavanono location, justifies an assessment of conservation status, according to IUCN (2001) Red List criteria, of Endangered (EN) B1ab(iii)+2ab(iii).

Figures

FIG. 1. — Floral and habit photographs of the three species of Megistostegium Hochr.: A, M. microphyllum Hochr.; B, M. nodulosum (Drake) Hochr.; C, M. perrieri Hochr. Scale bar for flowers: 2 cm.