Hibiscus ambanitazensis M. Hanes & G.E. Schatz, 2020

Hanes, Margaret M., Schatz, George E. & Callmander, Martin W., 2020, Transfer of the Malagasy genera Humbertianthus and Macrostelia to Hibiscus (Malvaceae) with description of four new species, Candollea 75 (2), pp. 193-202 : 197-198

Hibiscus ambanitazensis M. Hanes & G.E. Schatz , sp. nov. ( Fig. 1C ).

Holotypus: MADAGASCAR. Reg. Antsiranana [Prov. SAVA]: Com. Ampahana, Fkt. Andrapengy, Ambanitaza , 14°41'02"S 50°11'14"E, 9.XII.2015, fl., Razanatsoa, Bernard & Mashburn 644 ( MO-6710358 !; iso-: P, TAN).

Hibiscus ambanitazensis M. Hanes & G.E. Schatz is distinct from all other reddish, pendent flowered Hibiscus from the east coast of Madagascar in its petal pigmentation (purple red), and the combination of a long pedicel (up to 42 mm), epicalyx bracts with 6 lobes (fused at the base), and calyx fused to at least half of length (fused for 7–11 mm).

Shrub c. 3.5 m tall, sparsely branched; twigs covered with golden, semi-erect, simple, fascicled and stellate trichomes. Leaves 5.5–9.8 × 2.8–4.6 cm, elliptic to narrowly obovate, the base acute to obtuse, apex acuminate, the acumen to 0.8 cm long, the tip rounded, glabrous above, very sparsely covered with golden stellate trichomes below, venation weakly brochidodromous with 8–10 secondary veins per side, midvein raised above and below, secondary veins slightly raised above and below, tertiary venation finely reticulate, slightly raised above and below; petiole 8–11 mm, c. 0.8 mm in diam., moderately densely covered with semi-appressed, curly, light golden trichomes and occasional light golden stellate trichomes. Flowers solitary, axillary, pendent; pedicels 40–42 mm long, c. 0.8 mm in diam., densely covered with golden, erect, simple, fasciculate, and stellate trichomes; epicalyx with 6 lobes fused at the base for 3–4 mm of its length, the lobes 6 × 2.5–4 mm, ovate, the apex acute, densely covered with golden stellate trichomes on the outside, densely covered with golden appressed simple trichomes inside; calyx with 5 lobes, fused at the base for 7– 11 mm, the lobes c. 15 × 10 mm, ovate to triangular, the apex narrowly triangular, very densely covered with golden stellate trichomes outside and inside; petals 5, 30 × 14 mm, obovate, the apex rounded, purple-red, strongly reflexed, densely covered with white stellate trichomes outside, glabrous and verrucose inside with visible venation; staminal column c. 21 mm long, c. 1.8 mm in diam., red, sparsely to moderately densely covered with light golden stellate trichomes, with a tuft of dense golden erect simple trichomes at the apex; stamens c. 70, filaments 8–10 mm long, red, anthers c. 1.3 × 1.3 mm; styles 5, 12 – 15 mm long, white, sparsely covered with white trichomes, stigma c. 0.8 mm in diam., urceolate. Fruit unknown.

Distribution and ecology. – Hibiscus ambanitazensis is known from one collection in a forest fragment on volcanic soil (“table basaltique”) ( Fig. 2 ).

Conservation status. – Hibiscus ambanitazensis is known only by a single location outside of the Protected Area Network in a small patch of forest north of Antalaha in close proximity to recent slash and burn activity. The “table basaltique” along the east coast of Masoala to north of Antalaha are highly threatened because their rich volcanic soils are highly suitable for agriculture. The new species is assigned a conservation status of “Critically Endangered” [CR B2ab(iii)] using the IUCN Red List Categories and Criteria ( IUCN, 2012).

Notes. – The new species differs from all other reddish, pendent flowered Hibiscus from the east coast of Madagascar in its petal pigmentation, purple red (vs. red). Epicalyx, calyx and style color further distinguish H. ambanitazensis from H. ankeranensis , H. calyculatus and H. laurinusus (see Table 1 ).

Figures

Fig. 1. – Photographs of flowers of Hibiscus L. A. Hibiscus calyculatus (Hochr.) M. Hanes, G.E. Schatz & Callm.; B. Hibiscus laurinus Baill.; C. Hibiscus ambanitazensis M. Hanes & G.E. Schatz.

Fig. 2. – Known distribution of the seven species of Hibiscus L. highlighted in this paper.