Hydriastele biakensis W.J.Baker & C.D.Heatubun, Palms 56(3): 144-150 (2012)

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Distribution

Map uses TDWG level 3 distributions (https://github.com/tdwg/wgsrpd)
New Guinea present (Baker, W.J. & Heatubun, C.D. 2012: New Palms from Biak and Supiori, Western New Guinea. – Palms; Journal of the International Palm Society 56(3): 131-150)A
Known from few specimen localities and sight records on the south and western coast of Biak and Auki Island on the nearby Padaido Islands. (Baker, W.J. & Heatubun, C.D. 2012: New Palms from Biak and Supiori, Western New Guinea. – Palms; Journal of the International Palm Society 56(3): 131-150)A

Habitat

  • Coastal forest on limestone near to sea level, sometimes on limestone cliffs close to the beach. (Baker, W.J. & Heatubun, C.D. 2012: New Palms from Biak and Supiori, Western New Guinea. – Palms; Journal of the International Palm Society 56(3): 131-150)A

Diagnosis

  • Hydriastele biakensis is distinguished from other species in the genus by its large size, the recurving leaves with ascending leaflets and acute or notched leaflet apices, the often somewhat distorted prophyll bearing pronounced pithy keels, the peduncle abruptly constricting at the prophyll scar, the inflorescence branched to four orders, the highly sinuous rachillae, and the congenitally open staminate flowers. (Baker, W.J. & Heatubun, C.D. 2012: New Palms from Biak and Supiori, Western New Guinea. – Palms; Journal of the International Palm Society 56(3): 131-150)A

Conservation

  • Endangered (EN B1, 2 (a, b [i, ii, iii, iv, v]), C2a (i); IUCN 2001). This species is known only from coastal limestone forest which is severely degraded on Biak, especially on the south coast. Larger populations have been observed on the west coast and Padaido Islands. (Baker, W.J. & Heatubun, C.D. 2012: New Palms from Biak and Supiori, Western New Guinea. – Palms; Journal of the International Palm Society 56(3): 131-150)A

Common Name

  • Arwaf (Biak dialect) (Baker, W.J. & Heatubun, C.D. 2012: New Palms from Biak and Supiori, Western New Guinea. – Palms; Journal of the International Palm Society 56(3): 131-150)A

    Uses

    • The stem is used for flooring and the leaf sheaths for making baskets. (Baker, W.J. & Heatubun, C.D. 2012: New Palms from Biak and Supiori, Western New Guinea. – Palms; Journal of the International Palm Society 56(3): 131-150)A

    Description

    • Robust, solitary, canopy palm. Stem ca. 15 m tall, ca. 30 cm in diam., leaf scars prominent, internodes 3-7 cm, surface brown. Leaves ca. 18-24 in crown, strongly recurved; sheath ca. 170 cm long, pale green with white waxy indumentum, striate near mouth, forming crownshaft 200-270 cm long, 26-27 cm wide; rachis 280-300 cm long, petiole 47-50 cm long, 3.5-5 cm wide, channeled adaxially, petiole and lower rachis yellowish green, petiole and rachis bearing scattered to dense brown, caducous, felty indumentum and minute dark dots throughout; leaflets ca. 65 each side of rachis, regularly arranged, strongly ascending, concolorous, with minute dark dots abaxially, brown, basifixed ramenta attached to basal, abaxial portion of midrib; middle leaflets 121-126 cm long, 3-4.5 cm wide, linear, transverse veinlets conspicuous, apices narrowly acute; terminal segments linear, with apices notched, not praemorse. Inflorescence 95?100 cm long, infrafoliar, ?protandrous, horsetail-shaped, erect, branched to 4 orders, axes white on emergence, turning green; prophyll 70-107 cm long, 15-18 cm wide, green, often somewhat sinuous, appearing distorted, keels pithy, with thin, white with thin, white indumentum; first peduncular bract, ca. 70 cm long, ca. 5.5 cm wide, similar to prophyll, attached 2.5-4.5 cm above prophyll insertion; peduncle 10-21 cm long, 8-8.5 cm wide at base, narrowing sharply above prophyll insertion to 3-3.5 cm, prophyll scar conspicuous with rounded "shoulders"; primary branches 20-22, the longest (basalmost) to 70 cm; rachillae 32-48 mm long, 2-3 mm in diam., sinuous, especially distally, triads 2-3 mm apart, decussate. Staminate flower 5-6.5 mm long, 2.5-4 mm in diam. in bud, variously flattened and distorted, congenitally open; sepals connate in a shallow cup with three triangular lobes ca. 0.5 mm long, white; petals 5-6 mm long, 1-1.5 mm wide, narrowly triangular, variously twisted and sinuous, briefly adnate to receptacle, white; stamens 6, 4.5-5.5 mm long, white; filaments ca. 0.5 mm long, narrowly conoid; anthers 4-5 mm long, 0.8-1.2 mm wide, oblong to sinuous, basifixed, dehiscence latrorse; pistillode minute, pyriform. Pistillate flower ca. 2.5 mm long, 2.5-2.8 mm in diam., borne throughout the rachillae; sepals imbricate, ca. 1 mm long, 2.5-2.8 mm wide, rounded, white; petals 2-2.5 mm long, 2.5-3 mm wide, strongly imbricate, rounded, white; staminodes 3, minute, paddle-shaped; gynoecium ca. 2 mm long, ca. 1.5 mm in diam., globose; stigma minutely trifid. Fruit 9.5-12 mm long, 5-6 mm in diam., oblongellipsoid, red, perianth cupule clasping, endocarp thin, tough, closely adhering to seed. Seed 7.5-8.2 mm long, 4-4.3 mm in diam., cylindrical; endosperm homogeneous; embryo basal. (Baker, W.J. & Heatubun, C.D. 2012: New Palms from Biak and Supiori, Western New Guinea. – Palms; Journal of the International Palm Society 56(3): 131-150)A

    Materials Examined

    • Indonesia, Papua, Biak Island: Oridek district, Wadibu village, July 2009, Baker et al. 1342 (holotype K, isotypes AAU, BO, MAN), Heatubun et al. 970 (BO, K, MAN, NY). A sterile specimen may also represent this species: northern Biak, Wari village, September 1998, Maturbongs et al. 574 (BO, K, MAN). (Baker, W.J. & Heatubun, C.D. 2012: New Palms from Biak and Supiori, Western New Guinea. – Palms; Journal of the International Palm Society 56(3): 131-150)A

    Notes

    • We became aware of this beautiful species during the brief visit to Biak in 2000 (Baker pers. obs.) when it was seen cultivated near the now ruined Marau Beach Hotel and persisting wild as a few scattered individuals in cleared areas near the south coast. At that time, it was regarded as a species of Gulubia (now a synonym of Hydriastele) and suspected to be undescribed when compared with the species treated in Essig's (1982) monograph of the genus. Unable to collect material at that time, we had to wait until 2009 for an opportunity to make complete specimens for herbarium and laboratory study.
      To determine the relationships of the new species, we exploited an earlier phylogenetic study of Hydriastele (Loo et al. 2006). Following the protocols of Loo et al., we generated new DNA sequence data for H. biakensis of the two low-copy nuclear genes PRK and RPB2, integrated these new data within their published dataset and repeated their analyses. Hydriastele biakensis was strongly supported as sister species of H. palauensis. There are morphological similarities between the two species in general appearance, such as the strongly recurved leaves, ascending leaflets with acute or notched (but not conspicuously praemorse) apices and the glaucous crownshaft. The two also share the unusual feature of the staminate flowers being congenitally open in bud due to the large size of the stamens relative to the petals (Fig. 18). This character, alongside fruit structure, was considered diagnostic for the genus Gulubiopsis in which H. palauensis was originally described (Beccari 1924, Beccari & Pichi-Sermolli 1955). Moore and Fosberg (1956) deemed these features inadequate to justify generic status, reducing Gulubiopsis into synonymy with Gulubia, which was later sunk into Hydriastele (Baker & Loo 2004).
      In addition to morphological similarities, the two species occupy similar coastal limestone habitats. Moreover, Biak is among the closest of the Malesian islands to Palau, although almost 1000 km of clear ocean exists between the two. Nevertheless, the two are clearly distinct species. Hydriastele biakensis is much more robust than H. palauensis, for example with stem diameter, leaf length, leaflet number, leaflet length, sheath length and inflorescence being twice the size or more in the former than that reported for the latter (Moore & Fosberg 1956, Essig 1982). The contrast is most clear in the inflorescence which, as well as being much smaller in H. palauensis, lacks the striking "shoulders" formed by the abrupt constriction of the peduncle at the prophyll scar, and the highly sinuous rachillae (see p. 107), and in the material available to us (Lorence et al. 8304 [PTBG]) is branched to two rather than four orders. (Baker, W.J. & Heatubun, C.D. 2012: New Palms from Biak and Supiori, Western New Guinea. – Palms; Journal of the International Palm Society 56(3): 131-150)A

    Bibliography

      A. Baker, W.J. & Heatubun, C.D. 2012: New Palms from Biak and Supiori, Western New Guinea. – Palms; Journal of the International Palm Society 56(3): 131-150