Xerochlamys itremoensis, Hong-Wa, 2009

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 : 330-332

7. Xerochlamys itremoensis

Hong-Wa, G.E.Schatz & Lowry, sp. nov. ( Fig. 5 )

Arbuscula prostrata , caulis rubris, ramis junioribus pilosis, foliis ellipticis glabris ad apices acutis et ad bases attenuatis, floribus axillaribus solitariis.

TYPUS. — Madagascar. Prov. Fianarantsoa, Itremo, Massif de l’Itremo, Antsirakambiaty, végétation basse à Pachypodium brevicaule dominée par Xerochlamys , sol sommaire sur quartzite, 20°35’34”S, 46°34’18”E, 1830 m, 27.III.1999, fr., Labat et al. 3057 (holo-, P!, iso-, G, K, MO!, P!, TAN!).

PARATYPES. — Madagascar. Prov. Fianarantsoa, Itremo , [20°32’S, 46°33’E], 1500-1685 m, I.1964, Bosser 18879 ( MO, P, TAN) ; Bosser 18879bis ( MO, P, TAN) ; Bosser 18879ter ( P) . — 27. I.1975, Croat 29827 ( MO, TAN) ; Croat 29851 ( MO, TAN) . — 12. I.1973, Guillaumet 4259 ( P) . — Massif de l’Itremo, Ianasana , 20°34’40”S, 46°35’11”E, 1558 m, 25. VI.2005, Hong-Wa et al. 359 ( MO, P, TAN) . — Idem , [20°36’S, 46°39’E], 1500- 1700 m, 17.I-22.IV.1955, Humbert 28175 ( MO, P) . — [20°32’S, 46°33’E], 1.XII.1970, Keraudren-Aymonin 25788 ( MO, P) ; Keraudren s. n. ( MO, P) . — 1300- 1600 m, XI.1970, Morat 3655 ( P, TAN) . — 20°36’47”S, 46°34’44”E, 1710 m, 23.III.1996, Rakotomalaza et al. 671 ( MO) . — [20°36’S, 46°32’30”E], 1700 m, 6.VII.1992, A. Randrianasolo 237 ( MO) — Idem, eastern margin of the Itremo Massif, c. 19 km west of Ambatofinandrahana , 20°34’21”S, 46°34’54”E, 1580-1700 m, 10.III.2000, Schatz et al. 3959 ( MO, P) . — Idem , [20°36’S, 46°34’E], 1600-1700 m, 27.XI.1969, Service Forestier 28898 ( MO, P) . — Mt. Ambatomenaloha (Itremo massif), [20°37’S, 46°33’E], 17. I.1955, Service Forestier 11558 ( MO, P) .

DESCRIPTION

Shrubs prostrate; young twigs tomentose, older twigs glabrous. Leaf blades glossy green above, green to yellowish beneath, narrowly elliptic, 1-2 × 0.3- 0.6 cm, chartaceous, glabrous, base cuneate, margin plane, apex acute, midrib red, slightly sunken above, distinctly raised beneath, secondary veins conspicuous, 7-9 per side, 2-2.5 mm apart, looping c. 0.7 mm from the margin; petiole 1.8-2.1 mm long, glabrous. Flowers solitary, axillary; peduncle 2-6 mm long, with short indumentum, pedicel 1-2 mm long, short tomentose; involucre brown, urceolate, 3.5-5 × 4-5 mm, glabrous (with sparse white trichomes), teeth 11-17, 1- 2 mm long; flowers 15-20 mm long at anthesis from apex of pedicel to apex of petals; sepals oblong, 6-10 × 3-5 mm, slightly emarginate, exserted 3-4 mm beyond the involucre; petals pink to white, oblong, 12-13 × 5-6.5 mm, exceeding the involucre by 8-9 mm; disc 2 mm tall; stamens 30, 6- 10 mm long; ovary globose to ovoid, 3 mm high, style 7-10 mm long, basally pubescent, stigma 1-2 mm wide. Fruits subglobose to ovoid, 5-8 × 4.5-6 mm, exserted 1-2 mm beyond the accrescent involucre; seeds black, ellipsoid, 2-4 mm long, 4-7 per fruit.

PHENOLOGY

Flowering and fruiting from November to April.

HABITAT

Woodland at 1300-1800 m elevation, on quartzite, marble, and metamorphic and igneous rocks in the subhumid bioclimatic zone.

DISTRIBUTION

Known only from the Itremo massif ( Fig. 1 ).

REMARKS

This species can be recognized by its prostrate habit, its glabrous, narrowly elliptic leaf blades less than 1 cm across with an acute apex, and its solitary, pink to white flowers. Observations in the field indicate that this species grows in close proximity with X. diospyroidea but differs by its prostrate (vs. erect) habit, its glabrous (vs. pubescent), narrowly elliptic (vs. ovate) leaf blades and its solitary flowers (vs.flowers borne in inflorescences).It likewise differs from X. bojeriana and X. elliptica , which are erect shrubs with wider leaf blades that are respectively pubescent and glabrous. Unlike X. diospyroidea , the latter two species have not been seen growing in the same habitat as X. itremoensis , although they occupy the same general area.

CONSERVATION STATUS

With an area of occupancy of 54 km 2, an extent of occurrence no larger than that, and two subpopulations, neither occurring within a protected area, Xerochlamys itremoensis is assigned a preliminary status of Endangered [EN B1ab(i,ii,iii,iv)+2ab (i,ii,iii,iv)].

Xerochlamys itremoensis and X. diospyroidea are known only from the Itremo massif in central Madagascar. This massif, characterized by quartz and marble outcrops, harbours many locally endemic plants (e.g., succulents, palms, and orchids) that are regularly affected by bush fires, intensive exploitation and marble mining. Because of its unique vegetation and the high level of threat, the Itremo massif has been identified as a top priority for conservation ( Birkinshaw et al. 2004), and is now being represented among the “Système d’Aires protégées de Madagascar ” (SAPM).

Figures

FIG. 5. — Xerochlamys itremoensis Hong-Wa,G.E.Schatz & Lowry:A, flowering branch; B, leaf;C, flower bud;D, fruit; E, seed.Service Forestier 28898. Scale bars: A, 1 cm; B-D, 5 mm; E, 4 mm.

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]).