Pandanus tsingycola Callm. & Nusb., 2013

Callmander, Martin W., Bolliger, Ralph, Hanitrarivo, R. Mitia & Nusbaumer, Louis, 2013, Pandanus tsingycola Callm. & Nusb. (Pandanaceae), a new species endemic to western Madagascar, Candollea 68 (2), pp. 229-235 : 233-234

Pandanus tsingycola Callm. & Nusb. , spec. nova ( Fig. 2-3 ).

Typus: MADAGASCAR. Prov. Mahajanga: Beanka, partie sud, Andoloposa , 18°00’52”S 44°29’56”E, 255 m, 20.III. 2012, fr., Hanitrarivo, Bolliger & Rakotozafy 376 (holo-: G [ G00341180 , carpo]! ; iso-: MO!, P [ P00836310 , P00700 913 carpo]!, PH!, TEF!) .

Haec species a congeneris madagascariensibus syncarpio ex phalangibus grandibus perpaucis (7 ad 9) incomplete connatis maturitate secedentibus constante, quaque phalange ex carpellis (21 ad) 27 ad 33 (ad 38) constante, quoque carpello ad apicem in pileum pyramidalem abiente atque pileis ad cristas apicales vel ad marginem paginae apicalis truncatae stigmate solitario erecto curvatove acuto spiniformi praeditis distinguitur.

Treelet to 3-5 m tall, generally decumbent on tsingy, stem prickly, up to 8 cm diam., dried leaves persistent, pending below the crown of green leaves, surrounding the stem. Leaves 110-170 cm long, 2.5-3.7 cm wide in the middle, 3.5-4 cm wide near the sheath, gradually attenuate in the upper part, flagellate (ca. 20 cm long), coriaceous; longitudinal and transverse veins visible on both surfaces; prickles white in vivo; marginal prickles beginning at (6-) 7-8 cm above the base and extending to the apex, antrorse (rarely retrorse in the lower 1/3), 4-5 mm in the lower third, 2-5(-10) mm apart, strong, to 1-3 mm in the mid third; 4-10(-12) mm apart, to <1 mm in the distal third, 2-3 mm apart; midrib armed in the upper 2/3, prickles small (<1 mm), irregularly disposed (4-12 mm) in the middle, then regularly disposed, spaced (2-5 mm) as long as on the marginal in the distal 1/3; sheath 5 cm long, ca. 4-5 cm wide at apex ca. 9-11 cm large at base. Infrutescence terminal, a solitary syncarp pending at maturity, on a straight peduncle; syncarp 14-17 × 12-14 cm, irregularly shaped, the outline variable determined by the number and the position of the phalanges; peduncle (13-) 15-20 cm long, 1.5-2.2 cm wide at apex, 1.- 1.4 cm in the middle, straight, trigonous, veins visible, first bract borne 6-12 cm from the base of syncarp, 3-4 bracts scares along peduncle and the remaining bracts crowded at the base of the syncarp; lower bracts leaf-like, upper bracts boat-shape at base and flagellate in the distal part. Phalange, 6-7 per syncarp, (5-)6-7(-8) cm high, 9-11.5 cm wide, 5-6(-7) cm thick, (3-)4(-5) angled; carpels (21-)27-33 (-38), incompletely united, free in the upper ca. 1/5-2/5, tapering to the base; pileus divided by apical sinuses 1-2 cm deep into acute pyramids (sometimes slightly flattened at apex) as many as there are carpels. Stigma (21-)27-33(-38) per phalange (one per carpel), erect to curved, acute, thorny, on the apical ridges or on the edge of the truncate apical face of the pyramidal pileus, brown in vivo, generally prolonged by a sinus 0.6-1(-1.3) cm long towards the centre of the carpel, invaginated; endocarp 1.2-2.5 cm long in the centre, 1-2 cm wide, 1.5-2 cm away from the stigmas; seed locule oblong, 1-1.2 × 0.6-0.9 mm, superior and inferior mesocarp thick and fibrous. Staminate plant unknown.

Distribution. – Pandanus tsingycola is only known from the Beanka tsingy in western Madagascar ( Fig. 1 ). During botanical and vegetation studies in the region, several populations were observed on “tsingy”, and herbarium samples were collected at four study sites.

Habitat and ecology. – Pandanus tsingycola occurs on highly eroded limestone “tsingy” in plane areas with discontinuous soil, up to an altitude of 330 m. Pandanus tsingycola grows in primary dry decidous forests with open canopies reaching 12 to 15 m where the species is generally gregarious and sometimes comprises more than 90% of the vegetation cover ( Fig. 3A ). A study of the vegetation in Beanka (Rakotozafy & al., pers. comm.) based on 46 linear transects following the methodology of GAUTIER & al. (1994), showed that the new Pandanus is an indicator species sensu DUFRÊNE & LEGENDRE (1997) of the vegetation type described above refered to as “ Pandanus thicket”. This vegetation type is unique in their study in being characterized by the presence of a single (vs. numerous) indicator species. Furthermore, the species diversity is relatively low in “ Pandanus thicket” with only 98 different taxa vs. 180 to 339 taxa for the other four vegetation types (Rakotozafy & al., pers. comm.). The most frequently recorded species occurring with P. tsingycola in vegetation surveys include: Antiaris toxicaria subsp. madagascariensis (H. Perrier) C. C. Berg , Dioscorea antaly Jum. & H. Perrier , Givotia stipularis Radcl.-Sm. , Hildegardia erythrosiphon (Baill.) Kosterm. , Kirkia leandrii (Capuron) Stannard , Neobeguea leandriana J.-F. Leroy , Omphalea occidentalis Leandri , Poupartia sp., as well as Hymenodictyon leandrii Cavaco and Allophylus sp. , species that also occur in other vegetation types.

Conservation status. – With only four collections known and five reliable field observations, an “Extent Of Occurrence” (EOO) of ca. 19 km 2, an “Area Of Occupancy” (AOO) of 54 km 2 and two subpopulations (calculation following CALLMANDER & al., 2007), within the new Protected Area of Beanka with a temporary protection status, Pandanus tsingycola is assigned a preliminary status of “Vulnerable” (VU D2) ( IUCN, 2012).

Notes. – Pandanus tsingycola is morphologically unique among the genus. The new species bears syncarps with very few (7-9) incompletely fused phalanges which detach at maturity ( Fig. 2 ). The general shape of syncarp is irregular, its outline variable - determined by the number and the position of the few phalanges ( Fig. 2 ). Each of these phalanges is composed of (21-)27-33(-38) pyramidal carpels, with a single erect to curved, acute, thorny stigma, on the apical ridges or on the edge of the truncate apical face of this pyramidal pileus ( Fig. 3 ). The overall morphology of its phalange recalls those of P. biceps B. C. Stone & J.-L. Guillaumet and to some extent to P. nusbaumeri Callm. & L. Gaut. Both occur in the extreme north of Madagascar: P. biceps is endemic to the Ankarana massif ( STONE & GUILLAUMET, 1970) and P. nusbaumeri is endemic to the western leeward side of the Montagne d’Ambre ( CALLMANDER & al., 2009). All three species have incompletely united phalanges formed by several individual carpels with a more or less pyramidal pileus. However these species differ from the new species by several morphological characters (see Table 1 ).

Paratypi. – MADAGASCAR. Prov. Mahajanga: Beanka, Partie N, Ambabaky , 17°52’22”S 44°29’06”E, 185 m, 23.I.2012, fr., Bolliger, Hanitrarivo & Rakotozafy 121 ( G [ G00341216 ], FI, P, MO, TEF) ; Beanka, Partie N, Ambabaky , 17°53’20”S 44°29’31”E, 303 m, 17.XI. 2011, fr., Gautier, Tahinarivony & Bolliger 5635 ( G [ G00340555 ], TEF) ; Beanka, Partie N, Ambabaky , 17°52’29”S 44°29’19”E, 221 m, 14.XII. 2011, fr., Nusbaumer & al. 3117 ( G [ G00341179 ], K, TEF) .

Figures

Fig. 2. – Pandanus tsingycola Callm. & Nusb. A. Tip of a leaf; B. Median section of a leaf; C. Basal section of a leaf; D. Syncarp; E. Single carpel detached from a phalange; F. Cross section of a single carpel; G. Phalange; H. Cross section of a phalange. [Nusbaumer & al. 3117, TEF] [Drawing: R. Andriamiarisoa]

Fig. 3. – Pandanus tsingycola Callm. & Nusb. A. Ecology on tsingy; B. General habit; C-D. Syncarp. [A, C: Bolliger & al. 121; B, D: Hanitrarivo & al. 376] [Photos: A, C: R. Bolliger; B, D: R. M. Hanitrarivo]

Fig. 1. – Distribution of Pandanus tsingycola Callm. & Nusb. in Madagascar with highlight on the remaining forests on Mesozoic limestones on the whole island (right) as delimited by MOAT & SMITH (2007) and of the forested areas on the detailed map of the Beanka region (left). Ankarana and Bemaraha are highlighted.