Hydriastele gibbsiana (Becc.) Baker & Loo (2004: 65)

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

16. Hydriastele gibbsiana (Becc.) Baker & Loo (2004: 65) . Kentia gibbsiana Beccari (1917: 91) . Gronophyllum gibbsianum (Becc.) Moore (1963: 264) . Type:— INDONESIA. West Papua Province: Arfak Mts., Anggi Lakes, forest slopes and ridges by lake, 2150–2450 m, 1°23’S, 133°55’E, December 1913, Gibbs 5951 (holotype FI!, isotypes BM! K!, L!)

Figure 36 (line drawing). Figure 37 (photo plate). Figure 35 (map).

Solitary, moderately robust, emergent palm to 30 m tall, bearing 13–15 leaves in crown. Stem strongly ventricose, ca. 10 cm in diam. immediately below crownshaft widening to 20–30 cm in diam. further down, inner wood conspicuously soft and pithy; internode 1.5–6 cm long. Leaf 2–2.15 m long including petiole; sheath 60–82 cm long, sparsely or densely covered with a thin layer of lanate, orange-brown indumentum, crownshaft ca. 100 × 15 cm; petiole ca. 30 cm long, flattened adaxially; rachis arcuate; leaflets 50–53 per side, arranged regularly, ascending and ± drooping at their tips, linear, with ramenta on the abaxial, basal portion of the midrib; basal leaflets single-fold, acuminate or obliquely praemorse apically; middle leaflets 50–80 × 2–5 cm, single-fold, obliquely praemorse or acuminate and briefly bifid apically; terminal leaflets comprising 1–5 folds, truncately praemorse. Inflorescence 55–60 cm long including 4–5 cm peduncle, branched to 2 orders, protandrous; rachillae 22–28; triads on average 7–8 mm apart, opposite and decussate; inflorescences ca. 13 present. Staminate flower 11–16 × 2–4 mm in bud, cream; stamens 6–9. Pistillate flower 4–5 × 3–3.5 mm in bud, cream, with free sepals and free petals with conspicuous, triangular and valvate tips. Fruit ca. 13.5 × 8 mm when ripe, broadly ellipsoid, red, with a distinct, dark, sclerotic zone encircling apical stigmatic remains (up to ca. 3.5 mm in diam.). Seed ca. 9 × 6.5 mm, broadly ellipsoid; endosperm homogeneous.

Distribution:— Tamrau Mountains and Arfak Mountains of the Bird’s Head Peninsula, western New Guinea.

Habitat:— Premontane and montane rainforest on slopes and ridge tops, 950–2450 m.

Uses:— The very light and pithy trunks used for making rafts on the Anggi Lakes ( Fig. 38 ; Matthew Jebb pers. comm.) and for flooring in the Tamrau Mountains. Leaves used as thatch.

Vernacular names:— Syah (Madik).

Conservation status:— Data deficient (DD). The distribution and abundance of this species are insufficiently known.

Specimens examined:— INDONESIA. West Papua Province: Tambrouw Regency, Bamusbama Distr., forest along road to Fef east of Bamusbama , 950 m, 0°45’S, 132°16’E, 28 January 2013, Baker et al. 1379 (BO, K!, L, MAN); Arfak Moutains, Anggi Lake , forest slopes and ridges by lake, 2150–2450 m, 1°23’S, 133°55’E, December 1913, Gibbs 5951 (BM! FI!, K!, L!) .

Notes:— Hydriastele gibbsiana stands out among all New Guinea palms on account of its strikingly swollen stem. It is also a tall palm with relatively short (2–2.15 m), arching leaves and ascending leaflets with the terminal leaflet pair being multi-fold and truncately praemorse at the tip. The ventricose part of the stem is composed of soft, pithy and light inner wood with very wide vessels, and the inflorescence is relatively short (55–60 cm long) including a short (4–5 cm long) peduncle. Hydriastele gibbsiana is most similar to H. ledermanniana , although that species does not have a ventricose stem and its leaves and inflorescences are usually larger. Three other species of Hydriastele have conspicuously ventricose stems, H. procera , H. wosimiensis and H. ramsayi , but to a lesser extent. Only the two former occur in New Guinea and are distinguishable immediately from H. gibbsiana by their more-or-less straight leaves with pendulous leaflets.

On the Anggi Lakes, the stems of Hydriastele gibbsiana were, at least until the 90s, lashed together to make rafts, the pithy stems being very light and buoyant when dried (Matthew Jebb pers. comm.). Surprisingly, Gibbs (1917) made no reference to this in her account of the Arfak Mountain flora, but she did include a picture of a loaded raft that appears to be made of the trunks of H. gibbsiana ( Fig. 38 ). When Matthew Jebb returned to the Anggi Lakes in June 2017 he could no longer observe the trunks being used in this way (Matthew Jebb pers. comm.). The practice of using the stems for rafts may have contributed to the decline of local populations of this species.

Figures

FIGURE 35. Distribution map of the Longispatha group of Hydriastele in New Guinea and adjacent islands.

FIGURE 36. Hydriastele gibbsiana. A. Habit. B. Leaf apex. C. Mid-leaf portion adaxial side. D. Mid-leaf portion abaxial side. E. Inflorescence with pistillate flowers. F. Portion of rachilla with triads. G. Staminate flower in longitudinal section. H. Pistillate flower whole and in longitudinal section. I. Portion of rachilla with fruit. J. Fruit in longitudinal section. Scale bar:A = 1.5 m; B–D = 6 cm; E = 4 cm; F = 1 cm; G = 7 mm; H = 4 mm; I–J = 1.5 cm. All from Baker et al. 1379. Drawn by Lucy T. Smith.

FIGURE 37. Hydriastele gibbsiana. A. Habit. B. Inflorescence and infructescence. C. Portions of rachillae with triads. D. Portions of rachillae with fruit. A from the Anggi Lakes of the Arfak Mts., western New Guinea; B–D from the Tamrau Mountains, western New Guinea. Photos A: André Schuiteman; B–D: W.J. Baker.

FIGURE 38. Stems of Hydriastele gibbsiana lashed together to form rafts. Used by the Alfueros on both the Anggi Lakes (Gibbs 1917). Photo:A.E. Pratt. Reproduced from Gibbs (1917).