Hydriaste biakensis Baker & Heatubun (2012: 144–150)

Petoe, Peter, Heatubun, Charlie D. & Baker, William J., 2018, A monograph of Hydriastele (Areceae, Arecaceae) in New Guinea and Australia, Phytotaxa 370 (1), pp. 448-450 : 448-450

24. Hydriaste biakensis Baker & Heatubun (2012: 144–150) . Type:— INDONESIA. Papua Province: Biak Island, Oridek distr. , Wadibu village , 1°8’32”S, 136°18’11”E, July 2009, Baker et al. 1342 (holotype K!, isotypes AAU!, BO, MAN)

Figure 52 (line drawing). Figure 53 (photo plate). Figure 54 (map).

Solitary, robust palm to ca. 15 m tall bearing 18–24 leaves in crown. Stem ca. 30 cm in diam. Leaf ca. 3.3–3.6 m long including petiole; sheath ca. 170 cm long; petiole ca. 47–50 cm long; rachis strongly arcuate; leaflets ca. 65 per side, arranged regularly, single-fold, ascending and sometimes ± drooping at their tips, linear acuminate or sometimes briefly bifid to obliquely praemorse apically, with ramenta attached to the basal portion of the abaxial side of the midrib; middle leaflet 121–126 × 3–4.5 cm. Inflorescence 95–100 cm long including 19–21 cm peduncle, branched to 4 orders, apparently protogynous, with pronounced “shoulders” formed by the abrupt constriction of the peduncle right above the prophyll scar; prophyll often ± sigmoid, with pithy keels; rachillae sinuous, especially towards the tip; triads 3–7 mm apart, opposite and decussate. Staminate flower 5–6.5 × 2.5–4 mm in bud, white; stamens 6, exposed in bud. Pistillate flower ca. 2.5 × 2.5–2.8 mm in bud, with free sepals and free, low and ± rounded petals. Fruit 9.5–12 × 5–6 mm when ripe, narrowly ellipsoid, red, with inconspicuous sclerotic zone encircling apical stigmatic remains (up to ca. 1 mm in diam.). Seed 7.5–8.2 × 4–4.3 mm, cylindrical; endosperm homogeneous.

Distribution:— Numfoor Island and Biak Island. May also occur on the nearby Auki Island ( Baker & Heatubun 2012).

Habitat:— Coastal forest near beach or on cliff edges, on rugged limestone with very thin or no topsoil, near to sea level.

Uses:— Stems and leaf sheaths used for flooring and baskets respectively.

Vernacular names:— Arwaf (Biak).

Conservation status:— Endangered (EN; Baker & Heatubun 2012).

Specimens examined:— INDONESIA. Papua Province: Biak Island, Oridek distr., Wadibu village , 1°8’32”S, 136°18’11”E, 24 July 2009, Baker et al. 1342 (AAU!, BO, K!, MAN); Same locality as preceding, 1°8’32”S, 136°18’11”E, 24 July 2009, Heatubun 970 (BO!, K!, MAN!, NY!); Numfoor Island , 01°03’15.6” S 134°49’17.8”E, 11 November 2012, Heatubun 1225 (MAN, K!) .

Notes:— Hydriastele biakensis is endemic to the Biak Islands and is the only canopy species of the genus recorded from this area other than H. costata . Unlike H. costata , H. biakensis has a recurved crown, but differs from similar species in that its terminal leaflets are single-fold and pointed or shallowly notched at their tips (not truncately praemorse). In addition, its staminate flowers are congenitally open in bud and its prophyll is often somewhat distorted, features that are shared with the Australian H. ramsayi , but H. biakensis is distinguished from this, and all other species in the genus, by its inflorescence branched to 4 orders with markedly sinuous rachillae and a peduncle with prominent “shoulders” resulting from an abrupt constriction by the prophyll scar.

Hydriastele biakensis is strongly supported as sister species to the smaller H. palauensis ( Loo et al. 2006, Baker & Heatubun 2012), which is endemic to the Pacific island nation of Palau and, like H. biakensis , has staminate flowers that are congenitally open in bud (see Baker & Heatubun 2012).

Figures

FIGURE 52. Hydriastele biakensis. A. Leaf apex. B. Mid-leaf portion. C. Peduncle. D. Infructescence first order branch. E. Portion of rachilla with triads. F. Portion of rachilla with pistillate flowers. G. Staminate flower. H. Pistillate flower whole and in longitudinal section. I. Apical portion of rachilla with fruit. J. Fruit in longitudinal section.A–B, D = 6 cm; C = 8 cm; E, I = 1.5 cm; F, J = 1 cm; G = 5 mm; H = 3 mm. A–D from Baker et al. 1342; E–J from Heatubun et al. 970. Drawn by Lucy T. Smith.

FIGURE 53. Hydriastele biakensis. A. Habit. B. Crown. C. Inflorescence and peduncular bract contained within prophyll. D. Portion of rachilla with triads. E. Portions of rachillae with fruit.A–B from Biak Island; C–E from Baker et al. 1342. All photos W.J. Baker.

FIGURE 54. Distribution map of the Palauensis group of Hydriastele in Biak Island.