Pandanus imerinensis Martelli

Callmander, Martin W. & Laivao, Michel O., 2003, New findings on Pandanus sect. Imerinenses and sect. Rykiella (Pandanaceae) from Madagascar, Adansonia (3) 25 (1), pp. 53-63 : 54-55

Pandanus imerinensis Martelli

Webbia 2: 436, pl. 19 (figs. 16-18) (1907); Martelli & Pichi-Sermolli, Mém. Inst. Sci. Madagascar, Sér. B , Biol. Vég. 3: 166 (1951); Stone, Webbia 24: 588 (1970); Guillaumet, Webbia 28: 503, 506, fig. 4 (1), pl. 43 (2), pl. 48 (2) (1973); Stone, Bot. Jahrb. Syst. 94: 511 (1974). — Type: Rollot 10, Madagascar, Tamatave province, 1906 (holo-, FI!) .

Large trees 7-10 m tall, 16-20 cm in diameter at base, robust, straight, with 4-6 branches each ending in a clump of scythe-shaped leaves, prop roots forming a cone with the apex at 1-1.5 m above ground. Leaves caniculate, coriaceous, 75-80 cm (120-130 cm in pistillate plants) in length, 5 (-8) cm wide near the base, 3.5-4(-6) cm in the middle, with two auricles at base 6(-15) × 0.8 (-1) cm, acuminate, not flagellate; marginal prickles beginning 6(-15) cm from the base, 4(-6) mm long, up to 7(-10) mm apart, midrib armed with small prickles at 13(-20) cm from the base to the apex; when dried, abaxial face light brown, adaxial face dark brown, easily split apart at the midrib when flattened. Terminal inflorescence pendant in the middle of the clump of leaves; peduncle 73 cm long, 1.5 cm in diameter, spherical, hispid, bearing 11 bracts, the first three sterile; internodes 1-4 cm (7 cm between the first and the second); first bract born 23 cm from the base, all bracts lanceolate; the lowermost is 35 cm long, 4-5 cm wide in the middle; the midrib and the costal rib armed from 12 cm to the base with little prickles (0.3-0.5 mm long) up to 1-2 mm apart; bracts flexuous in the lower 1/4, then subcoriaceous, abortive in the last three inflorescences; subtending 14 inflorescence spikes (up to 17 cm long, 3 cm wide); flowers arranged densely in each spike of the inflorescence; 3-20 stamens per flower (the filaments is often fused); anthers 1.5 × 0.3 cm, mucronate, arranged at the apex of the filament; the filament is 6- 10 mm long, 0.7-1 mm wide, often fused (up to 5- 8 mm wide). Pollen grains obovoid to spherical, 20 µm long, spinulose, with an apical aperture.

MATERIAL STUDIED. — MADAGASCAR: Callmander & Bemandiny M122 (pistillate plant) , Callmander & Bemandiny M123 (staminate plant) , Maroantsetra, Nantoroka road, 15°27’57’’S, 49°40’31’’E, 5 Nov. 1999 ( G, NEU, P, TAN); Perrier de la Bâthie 13290, Tampina south of Tamatave , Nov. 1929 ( FI, P); Perrier de la Bâthie 14096, near Vatomandry , Nov. 1921 ( FI, P); Rollot 10, Tamatave province, 1906, type ( FI) .

NOTES. — This species occurs along the east coast of Madagascar, in swamps, often in secondary littoral forest from elevation 0-30 m ( Fig. 1 ). Its vernacular name is Bobaka in the Betsimsaraka language .

Pandanus imerinensis is a remarkable species. It was first placed by STONE (1970a) in Pandanus sect. Rykiella (subg. Rykia ) because of its comparable spiniform style ( Fig. 3B ), but later he assigned it to section Lonchostigma along with P. rollotii and P. peyrierasii ( STONE 1974) , altought he indicated that it was «… placed here with much doubt, for although the styles are comparable, other characters are greatly different; especially the multicephalic inflorescence on its long, hispid peduncle.» (cf. Figs. 3A, 3D ). HUYNH (1979a) then based his new monotypic sect. Imerinenses on this species, distinguishing it because of the micromorphology of leaves. With the discovery of a staminate plant, new arguments for the systematic and biogeographic position of P. imerinensis can be made.

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The staminate flowers of Pandanus species are not very useful in intraspecific comparison because of low variation of its morphology, a notable exception being subg. Martellidendron (cf. CALLMANDER 2001). They are however useful for differentiation between sections ( HUYNH 1977). Pandanus rollotii , whose ecology and morphology are close to members of Pandanus subg. Rykia , clearly belongs to subg. Vinsonia , largely because its staminate flowers have a candelabralike displacement of their stamens ( HUYNH 1977: 460, fig. 22) instead of the pseudo-umbel found in members of subg. Rykia ( STONE 1974). In Pandanus imerinensis , the staminate flowers also have a candelabra-like stamen disposition ( Fig. 6E ), but this is a result of secondary ramification of the stamen columns, whereas in Pandanus subg. Rykia the stamen column is never twice ramified (This is especially evident on the type of P. ceylanicus ( MARTELLI 1913: figs. 25-27, pl. 29). The anthers of P. imerinensis are small and mucronate ( Fig. 6F ), its pollen is spinulose ( Fig. 6D ), and its inflorescence holds many spikes ( Fig. 2 ), all characters that are common throughout the genus. Less frequent is the hispid peduncle ( Fig. 3D (a), 3D(b)), a rare character in Pandanus and unique to subg. Vinsonia . Furthermore, the micromorphology of the leaves is unique among Malagasy species in having stomata with ramified papillae of class VII following HUYNH (1974) ( Fig. 6C ). Its diffuse architecture with little ramification ( Fig. 3E ) is likewise unique in Madagascar described by GUILLAUMET (1973) as icon forming to Stone’s model, with lateral branches not limited in growth.

Figures

Fig. 1. — Map of Madagascar showing collection localities of members of Pandanus sect. Imerinenses (grey) and sect. Rykiella (black square). Major towns are indicated by a black circle.

Fig. 3 — Pandanus imerinensis: A, young pistillate inflorescence; B, lateral view of drupe showing the stigma; C, longitudinal section through the centre of the stigma showing locule and fleshy upper mesocarp; D, peduncle of an infrutescence showing its hispid surface (a) with a detail of the trichomes (b); E, habit showing typical diffuse architecture. (Callmander & Bemandiny M122). — Drawn by A. MEZOUAR.

Fig. 6. — LM (light microscopy) view of stomata on abaxial leaf surface (A-C) (scale bars = 20 µm) and SEM (scanning electron microscopy) of pollen and staminate flowers (D-F): A, stomata of Pandanus longissimepedunculatus showing papillae (Laivao et al. M034); B, stomata of Pandanus macrophyllus showing papillae (Callmander et al. M041); C, stomata of Pandanus imerinensis showing dendritic ramifications of papillae (Callmander & Bemandiny M122); D, spinulate pollen of Pandanus imerinensis (Callmander & Bemandiny M0122), scale bar = 5 µm; E, staminate flower of Pandanus imerinenses showing the candelabra-like disposition of stamens, scale bar = 2 mm; F, close up of a mucronate anther, scale bar = 500 µm (Callmander & Bemandiny M122).

Fig. 2. — Pandanus imerinensis, staminate inflorescence. (Callmander & Bemandiny M122).— Drawn by A. MEZOUAR.