Mediusella (Cavaco) Hutchinson

Hong-Wa, Cynthia, 2009, Endemic families of Madagascar. XII. Resurrection and taxonomic revision of the genera Mediusella (Cavaco) Hutchinson and Xerochlamys Baker (Sarcolaenaceae), Adansonia (3) 31 (2), pp. 311-339 : 315-318

Genus Mediusella (Cavaco) Hutchinson

The Families of Flowering Plants Arranged According to a New System Based on their Probable Phylogeny: 347-348 (1973). — Leptolaena subgen. Mediusella Cavaco , Bulletin du Muséum national d’Histoire naturelle, 2e sér., 23: 135 (1951). — Type: Leptolaena bernieri Baill.

DESCRIPTION

Small trees or shrubs; young twigs flattened, glabrous, older twigs glabrous, with white lenticels. Leaves simple, two-ranked, blades entire, without vernation traces, glabrous, coriaceous, narrowly to broadly ovate, base cordate, sometimes rounded, margin entire, usually plane and sometimes sinuate or revolute, apex often acute but sometimes obtuse or acuminate; petiole glabrous, canaliculate; stipules brown, glabrous, paired, free, early caducous. Flowers sometimes solitary or in inflorescences, terminal, cymose. Flowers shortly pedicelled, subtended by an involucre; involucre glabrous, woody, with 7-12 triangular teeth; sepals green, 3, obovate, deeply emarginate, persistent, imbricate, often abaxially densely pilose, adaxially glabrous, enclosed within the involucre; petals 5, obovate, contorted, glabrous, exceeding the involucre by 7-12 mm; disc annular, toothed; stamens> 20, in 1 or 2 whorls, filaments white to greenish, free, slender, of unequal length, anthers yellow, with 2 locules, opening by longitudinal slits; ovary superior, ovoid, with 3 locules, sulcate, pubescent, style green, slender, glabrous, stigma yellow, capitate. Fruits indehiscent, ovoid to globose, sulcate, usually enclosed within the woody involucre; pericarp intact at maturity; seeds black, ovoid, 1-4 per fruit.

KEY TO THE SPECIES OF MEDIUSELLA (CAVACO) HUTCHINSON

1. Leaf blades dull green beneath, sometimes broadly to often narrowly ovate, often abaxially folded along the midvein, smooth, the apex acute to acuminate; involucre thick, obconic, entirely or sometimes only partially enclosing the fruit; from Ankara (Besalampy) to Ambohipiraka .............................................................................................. 1. M. arenaria

— Leaf blades dull green to whitish beneath, broadly ovate, flat, sub-bullate, the apex acute to obtuse; involucre thin, oblong, only partially enclosing the fruit, which exceeds it by few millimeters; from Ankotekona to Vohémar ...................................... 2. M. bernieri

1. Mediusella arenaria (F.Gérard) Hong-Wa Xerochlamys arenaria F.Gérard, Comptes rendus de l’Association française pour l’Avancement des Sciences 1914 (sess. 43): 407 (1915). — Leptolaena arenaria (F.Gérard) Cavaco , Bulletin du Muséum national d’Histoire naturelle, 2e sér., 23: 135 (1951). — Type: Madagascar, Prov. Mahajanga, pentes très sèches et dénudées du Besafotra, affluent du Menavava (Boina), sur les gneiss, [17°04’S, 46°39’E], VI.1900, fl., Perrier de la Bâthie 1062 (holo-, P! [P00389109]; iso-, P! [P00389110]).

Xerochlamys acuminata F.Gérard, Comptes rendus de l’Association française pour l’Avancement des Sciences 1914 (sess. 43): 410 (1915). — Type: Madagascar, Prov. Mahajanga, Ouest, Marovato , Boina , bois secs, [17°00’S, 46°10’E], IV.1907, fl., Perrier de la Bâthie 3028 (holo-, P! [ P00490430 ]).

ADDITIONAL MATERIAL EXAMINED. — Madagascar. Prov. Antsiranana, Ambakirano, collines gréseuses sur la piste d’Ambilobe à Ambakirano , [13°14’S, 49°09’E], 9.III.1964, Service Forestier 23413 ( MO, P, TEF) . — Ambilobe , [13°11’30”S, 49°03’30”E], 1.VIII.1959, Decary s. n. ( TAN) . — Idem, 5 km d’Ambilobe sur route de Daraina , 13°11’33”S, 49°04’32”E, 72 m, 29. V.2005, Hong-Wa et al. 251 ( CNARP, MO, P, TAN) . — Idem, forêt à l’est d’Ambilobe , [13°11’30”S, 49°03’30”E], 17.X.1927, Ursch 274 ( P) . — Ambohipiraka, montagne d’Ambohipiraka , [13°06’S, 49°08’E], 5.II.1960, Cours & Humbert 5644 ( P) . — Idem, Mont Ambohipiraka au nord-est d’Ambilobe , [13°06’S, 49°08’E], 100-300 m, 3.II.1960, Humbert & Cours 32855 ( K, P) . — 3.II.1960, Humbert & Cours 32874 ( P) . — Anaborano, vallée de l’Ifasy en aval d’Anaborano , [13°34’S, 48°49’E], 50-200 m, 31.III.1951, Humbert & Capuron 25931 ( K, P) . — Bemofo [= Bemafo], [13°32’S, 49°04’E], 0-200 m, 3. VI.1954, Service Forestier 10437 ( MO, P, TEF) . — Ilevika, base des collines du Levika aux environs de Matsaborilava , [13°16’S, 49°01’E], 12.III.1951, Service Forestier 3053 ( K, MO, P, TEF) . — Prov. Mahajanga, Ampasimantera , [15°56’S, 47°44’E], XII.1906, Perrier de la Bâthie 3030 ( K, P) . — Ankara, massif de l’Ankara , [17°06’S, 46°06’E], 24.VII.1939, Decary 14538 ( P) . — Ankerefo , [16°47’S, 44°24’E], 18.III.1954, Service Forestier 9428 ( P, TEF) . — Betaramahamay, forêt sèche sur sable d’Ambohimanga , 15°57’05”S, 47°26’09”E, 232 m, 4.XII.2004, Razakamalala 1820 ( MO, P, TEF) . — Betaramahamay, forêt de Bongolava Sud, route vers Mampikony , [15°57’S, 47°24’E], 200 m, 28.IX.1960, Service Forestier 19787 ( P, TEF) . — Cap Saint André , [16°11’S, 44°27’E], 8. VI.1930, Decary 7881 ( P) . — Madirovalo, forêt de Tsimabeomby , 16°29’25”S, 46°33’52”E, 105 m, 10.VII.2005, Hong-Wa et al. 424 ( MO, P, TAN) . — Idem, collines sèches et sablonneuses aux environs de Madirovalo , [16°26’S, 46°32’E], III.1901, Perrier de la Bâthie 1062bis ( P) ; Perrier de la Bâthie 1062ter ( P) . — Majunga , [15°40’S, 46°40’E], I.1921, Perrier de la Bâthie 13475 ( P) . — Mampikony , [16°06’S, 47°38’E], I.1907, Perrier de la Bâthie 3029 ( P) . — Mariarano , [15°25’S, 46°39’E], VII.1921, Perrier de la Bâthie 13914 ( P) . — Réserve naturelle intégrale d’Ankarafantsika, Ankorika , [16°00’S, 46°56’E], 100-150 m, 4.IV.1933, Anonymous 35 ( TAN) . — 200 m, 31.VIII.1924, Humbert & Perrier de la Bâthie 2340 ( P) ; Service Forestier 35 ( MO, P) ; Service Forestier 58 ( P) ; Service Forestier 63 ( P) ; Service Forestier 75 ( P) ; Service Forestier 86 ( P) .

DESCRIPTION

Trees 4-12 m tall, trunk to 30 cm dbh. Leaf blades bright green above, dull green beneath, narrowly or sometimes broadly ovate, 4-7 × 1-4 cm, often abaxially folded along the midvein, smooth, base cordate, margin plane to somewhat sinuate, apex acuminate, sometimes acute, midrib light green, slightly raised above, distinctly raised beneath, secondary veins conspicuous, 7-10 per side, 2-7 mm apart; petiole 6-11 mm long. Flowers solitary, or more often grouped into inflorescences, terminal, with 2 flowers, peduncle 1.5-2.5 mm long, glabrous; pedicel 1-2 mm long, glabrous. Involucre green, urceolate to infundibuliform, 4-13 × 4-14 mm, 1-1.2 mm thick, teeth 7-(12), 1-2 mm long; flowers 15-25 mm long at anthesis from apex of pedicel to apex of petals; sepals 3-8 × 3-5 mm; petals white, 11-17 × 4-7 mm, exceeding the involucre by 8-12 mm; disc 2-2.5 mm tall; stamens 32-44, 6.5-12.5 mm long; ovary 3-4.5 mm high, style 4-9 mm long, stigma 1 mm wide. Fruits subglobose to globose, 6.5-12 × 7-12 mm, often entirely enclosed within the accrescent involucre; seeds 3-5 × 2 mm, 1-3 per fruit.

PHENOLOGY

Flowering and fruiting from January to August.

VERNACULAR NAMES

Sana, Zahana.

HABITAT

Low elevation (50-200 m) dry forests on white sands and sandstone within the dry bioclimatic zone recognized by Schatz (2000, after Cornet 1974).

DISTRIBUTION

From Cap St André to around Ambilobe in NW Madagascar ( Fig. 1 ).

REMARKS

Mediusella arenaria can be recognized by its glabrous, narrowly to sometimes broadly ovate, often abaxially folded leaves with a distinctly acute to acuminate apex, and its thick woody involucre enclosing the fruit often entirely or sometimes partially. These features distinguish M. arenaria from M. bernieri , its apparent closest relative and the only other member of Mediusella .

Mediusella arenaria was once placed within Xerochlamys by Cavaco (1952a, b). However, it lacks indumentum on the leaves; its involucre is woody rather than fleshy and has few teeth (c. 10 versus c. 20 in members of Xerochlamys ); and its pericarp does not dissociate with age. In all these features, M. arenaria is, however, similar to M. bernieri , and they are therefore placed together in Mediusella .

CONSERVATION STATUS

Mediusella arenaria is restricted to northwestern Madagascar, but is widespread from Cap St André to Ambilobe. However, despite a large extent of occurrence (85 202 km 2), its area of occupancy is only 198 km 2 and only four out of 20 subpopulations are found within protected areas (Réserve naturelle intégrale d’Ankarafantsika). This species is facing a continuing decline because of habitat destruction due to annual fires, wood exploitation and specificity of its substrate; it is assigned a preliminary conservation status of Near Threatened ( NT). The last recent collection was made in 2005 (Hong-Wa et al. 424) in the area where the type was collected in 1900; the visit revealed only three individuals .

Figures

FIG. 1. — Distributions of Mediusella arenaria (F.Gérard) Hong-Wa (▲), M. bernieri (Baill.) Hutchinson (✚), Xerochlamys itremoensis Hong-Wa, G.E.Schatz & Lowry (●) and X. undulata Hong-Wa (■) mapped on the bioclimatic zones of Madagascar (after Cornet [1974], simplified by Schatz [2000]).