Pandanus voradolii Callm. & Buerki, 2018

Callmander, Martin W. & Buerki, Sven, 2018, A new species and a new synonym in Pandanus subg. Rykia (Pandanaceae) in Thailand, Candollea 73 (1), pp. 115-120 : 117-119

Pandanus voradolii Callm. & Buerki , spec. nova ( Fig. 2 ).

Holotypus: THAILAND. Prov. Bueng Kan: Tham Fun waterfall , Phu Wua WS, 18°15’52”N 103°54’21”E, 345 m, 28.III.2014, fr., Callmander et al. 1163 ( BKF! ; iso-: BM!, G [ G00428130 ]!, K!, SRP-061977 !).

Pandanus voradolii Callm. & Buerki differs from its congeners by its rheophytic ecology, acaulescent shrubby habit with a crown of narrow, subcoriaceous and flagellate leaves; its subspherical to obovate small syncarp on a long, curved, slender peduncle with 200-280 drupes.

Rheophytic shrub along stream on sand, acaulescent to 1 m tall. A crown of erect leaves, pale green to glaucous below. Leaves 100-120 cm long, 2.5-3 cm wide in the middle, 2.8-3.2 cm wide near the sheath, attenuate distally on a short flagellum (c. 5 cm long), subcoriaceous; prickles white in vivo; marginal prickles beginning at 8-10 cm above the base and extending to the apex, antrorse, 2-2.5 mm in the lower third, (6-)9-15(-20) mm apart, strong, to 1.5-2 mm in the mid third; (15-)20-25(-35) mm apart, to <1 mm in the apical distal third, 4-11 mm apart; midrib armed at 8-11 cm above base, prickles strong in the lower part, c. 2.5 mm long, getting smaller through the apex, c. <1 mm long in the apical part (and sparsely arranged in the mid part); prickles discrete in the distal part, c. <1 mm long, irregularly spaced; sheath 6-7 cm long, 3.5-4 cm wide at apex, c. 5-6(-7) cm large at base. Infructescence lateral, monosyncarpic, pending at maturity, on a curved peduncle (rarely straight); syncarp 6-7(-8) × 6-7 cm, sub-spherical to obovate; peduncle with 5-7 caducous leafy bracts; proximal bract up to 80 x 3 cm, subcoriaceous, distal bract up to 30 x 2.5 cm; peduncle, slender, 50-65 cm long, 1-1.5 cm wide at apex, veins conspicuous. Drupes, c. 200-280 per syncarp, 20-25 mm high, 7-9 mm wide, 6-8 mm depth, 6 angled; pileus flattened to steeply pyramidal, pale green in vivo. Stigma unique, bony, bifurcate (rarely simple), brown, 5-6 x 2-3 mm; endocarp c. 10 x 4 mm; seed ellipsoid, 7-8 x 3 mm; proximal and distal mesocarp fibrous. Staminate plant unknown.

Etymology. – This species epithet honours Dr. Voradol Chamchumroon from the Forest Herbarium in Bangkok (BKF). Voradol is specialized in Thai Rubiaceae (especially the genus Ixora L. ; CHAMCHUMROON, 2004, 2006, 2014), but he has an overarching expertise of the Thai flora. His knowledge, enthusiasm, professionalism and dedication to the Thai flora lead to the discovery of this new species that the authors are honoured to name after him.

Distribution and ecology. – Pandanus voradolii is currently only known from three collections in north-eastern Thailand where it grows along streams on sands in dry evergreen forests.

Conservation status. – Pandanus voradolii is currently known from three locations occurring in the vast Thai protected area network, viz. Phu Phan National Park and Phu Wua Wildlife sanctuary. Despite of the rarity of this species, which is most likely due to under collecting, this new species does not seem to be threatened in the near future and we therefore assign it a provisional status of “Least Concern” [LC] using the IUCN Red List Criteria ( IUCN, 2012).

Notes. – In its acaulescent shrubby habit, this new species resembles P. obconicus . Pandanus voradolii can be nevertheless easily recognized by its subcoriaceous and narrow leaves (<3 cm vs> 4 cm and coriaceous in P. obconicus ), long and curved peduncle (50-65 cm vs 20-30 cm) and sub-spherical to obovate small syncarp (6-7(-8) × 6-7 cm vs oblong 8-14 × 5-8 cm) bearing 200-280 drupes (vs 400-500).

Based on its morphology, we assign P. voradolii to Pandanus subg. Rykia . Although this subgenus is polyphyletic and requires to be re-circumscribed ( BUERKI et al., 2012), the new species is assigned to the true Rykia ( Pandanus subsect. Rykia sensu STONE, 1974) with the type of this section, Pandanus furcatus Roxb. STONE (1982) accepted 7 native species of Pandanus subsect. Rykia including 2 possible new species for Thailand. The first of these putative new species refers to the unpublished name “Pandanus aphitrios H. St. John” based on Hansen et al. 11208 (C [C10016345]). To our knowledge, this unpublished name should be regarded as a synonym of P. reticulosus H. St. John. The second potential new species refers to the unpublished name “Pandanus hansenii H. St. John” based on Hansen et al. 11230 (C [C10016346]). This name belongs to a complex of morphologically closely-related species occurring in the mountains in the north and north-western Thailand described by ST. JOHN (1962, 1963): P. acaulescens H. St. John , P. ligulatus H. St. John and P. penetrans H. St. John. Only P. acaulescens and P. penetrans have been currently tentatively accepted ( CHAYAMARIT et al., 2014) in a first Pandanaceae checklist. Pandanus subg. Rykia is certainly the most species-rich subgenus in Thailand, but more field work in this region and nearby countries (e.g. Viet-Nam and Lao PDR) is required to establish a final taxonomic treatment.

Paratypi. – THAILAND. Prov. Bueng Kan: trail to Chet Si waterfall , Phu Wua WS , 18°09’32”N 103°56’55”E, 200 m, 11.III.2016, fr., Poopath et al. 1428 ( BKF) . Prov. Sakhon Nakhon: Phu Phan , [16°58’48”N 103°57’00”E], 30.XI.1962, fr., Phloenchit 1984 ( BKF, PH).

Figures

Fig. 2. - Pandanus voradolii Callm. & Buerki. A-B. Habit; C. Infructescence. [Photos: M. Callmander]