Helmiopsis rigida (Baill.) Dorr, 2001

Dorr, Laurence J., 2001, A new combination in the endemic Malagasy genus Helmiopsis (Malvaceae-Dombeyoideae), Adansonia (3) 23 (1), pp. 151-153 : 151-153

Helmiopsis rigida (Baill.) Dorr , comb. nov.

Dombeya rigida Baill., Bull. Mens. Soc. Linn. Paris 1: 487 (1885) [1 avril 1885]; Baron , Revue de Madagascar 3: 940 (1901); Palacky, Cat. 5: 28 (1907); Hochreutiner, Candollea 3: 60 (1926); Arènes, Candollea 16: 296 (1958); Arènes, Fl. Madag. 131: 233 (1959). — Type: Hildebrandt 3442, W Madagascar pr. Trabonji, mai 1880, fl. (holo-, P-2 sheets; iso-, G-DC, K!, US!) .

Dombeya guazumaefolia Baill., Bull. Mens. Soc. Linn. Paris 1: 495 (1885) [6 mai 1885]; Baron , Revue de Madagascar 3: 940 (1901); Palacky, Cat. 5: 27 (1907). — Type: Bernier 340 pro max. parte, 2 e env., Madagascar “Ad sin. Ling-vatou” (P-3 sheets).

ADDITIONAL MATERIAL EXAMINED. — MADAGASCAR, Mahajanga : Perrier de la Bâthie 5535, bords de l’Anjobona (Boeny), Aug. 1905, fl., fr. ( K, P); Service Forestier 31- SF, Tsingy de Namoroka, 8 e réserve ( BR, P); Service Forestier 3570- SF, bords de rivière Marofototra, route Befandriana-Nord, 4 June 1951, fl. ( K, P); Service Forestier 15772- SF, forêt d’Analamazava, Befandriana, 12 June 1956, fl., immature fruit ( K, P); Service Forestier 22630- SF, s.d., fl. ( BR, P, US) .

ARÈNES (1959: 234) referred other specimens to Dombeya rigida , but I have not had the opportunity to critically evaluate them in the context of this note.

The description of the fruit and seed of this species provided by ARÈNES (1959: 233-234) can be modified as follows: Capsule subglobose to depressed globose, depressed apically, rounded basally, more or less 5-lobed, 10-12 mm tall, 10- 15 mm in diameter, strongly papillate with papillae of irregular size, pale brownish-ferrugineous stellate-pubescent. Seeds 2 per locule, asymmetrically ovate or reniform, c. 3 mm long, 2.5 mm wide, laterally flattened, glabrous, lustrous, each with a narrow, 1-1.5 mm wide, membranous, dorsal wing.

The presence of papillae on the mature fruit of Helmiopsis rigida is somewhat problematic. While papillae are conspicuous in the one specimen with mature fruit ( Fig. 1 ), examination of the ovaries of flowering material fails to show papillae, even nascent ones. Additionally, papillae were not mentioned by either HOCHREUTINER (1926: 60-61) or ARÈNES (1959: 233-234), both of whom cited Perrier de la Bâthie 5535 (albeit not the sheet I examined at Kew). Furthermore, papillae are not seen on the fruit of other species of Helmiopsis , but then only four of the ten species recognized are known in fruit.

For most species of Helmiopsis the presence and position of seed wings have been inferred from ovule morphology. In the species where mature fruit are unknown, the ovules have apical wings 2-6 times as long as the ovule proper. In those species known from fruit, the seeds have either a pronounced, 4-30 mm long, apical wing ( H. hily Arènes and H. inversa H. Perrier ), a relatively inconspicuous, 1-1.5 mm long, dorsal wing ( H. rigida ), or a “narrow, membranous, ventral keel” ( H. sphaerocarpa L. Barnett ; BARNETT 1987).

In addition to this reduced seed wing, Helmiopsis rigida shares several other characters with H. sphaerocarpa . The inflorescences are multibranched and many-flowered, the capsules are spheroidal rather than conical, and the capsules have 2, laterally-flattened seeds per locule ( Helmiopsis hily evidently has only one, tetragonous seed per locule). Both species key ( ARÈNES 1959: 96) to Helmiopsis subg. Helmiopsis sect. Glandulipetalae Arènes. In H. rigida (as opposed to H. sphaerocarpa ), however, the inflorescence is terminal and axillary (versus terminal only), and glandular tissue occurs on the petals alone (versus on both the calyx lobes and petals).

Inclusion of Dombeya rigida in Helmiopsis modifies slightly a character that was thought to unite the genus (see e.g., ARÈNES 1959: 95-96; HUTCHINSON 1967: 506). Previously, all species of Helmiopsis had peltate scales that set them apart from the closely related Helmiopsiella . Helmiopsis rigida , with its more or less stellatehispidulous indumentum, would appear to be a remarkable exception but for the fact that H. cal- cicola (H. Perrier) Arènes, which has peltate scales, also has stellate-villous indumentum on the upper surface of its leaves. Moreover, the utility of indumentum as a generic character in the Malvaceae-Dombeyoideae recently was dispelled by JENNY et al. (1999).

Figures

Fig. 1. — Helmiopsis rigida, capsule and seed: A, capsule showing papillae; B, capsule locule showing the position of a seed and its wing. From Perrier de la Bâthie 5535 (K). — Drawn by A. TANGERINI.