Hydriastele rheophytica Dowe & Ferrero (2000b: 195)

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

5. Hydriastele rheophytica Dowe & Ferrero (2000b: 195) . Type:— INDONESIA. Papua Province: Idenburg River [Taritatu River], Araucaria Creek , 3°29’S, 139°6’E, March 1939, Brass 13700 (holotype A!, isotype L!)

Figure 10 (line drawing). Figure 11 (photo plate). Figure 4 (map).

Clustering, rheophytic palm forming clumps of as many as 30 stems, slender, to 6 m tall, bearing 4–12 leaves per crown. Stem 2–2.5 cm in diam., pliable and mostly leaning. Leaf ca. 95–120 cm long including petiole; sheath 40–45 cm long, petiole 20–30 cm long, pliable; leaflets 18–32 per side, arranged regularly, linear, thin and soft; basal leaflets single-fold, obliquely praemorse apically; terminal leaflets comprising 2 or 3 folds, truncately praemorse apically. Inflorescence 16–30 cm long including 2.5–7 cm peduncle, branched to 1 or 2 orders, protogynous; rachillae 5–15 per inflorescence; triads opposite and decussate. Staminate flower 6–8 × 3–4 mm (when dry); stamens 6. Pistillate flowers 2–2.5 × 2 mm in bud (when dry), with free sepals and free, ± rounded, low petals. Fruit ca. 7 mm long, globose to broadly ellipsoid, with inconspicuous stigmatic apical remains lacking encircling dark sclerotic zone. Seed globose; endosperm shallowly ruminate.

Distribution:— Known from the Idenburg River and its upper tributaries in Papua Province, western New Guinea.Also reported from the Frieda River in the adjacent Sandaun Province of Papua New Guinea ( Dowe & Ferrero 2000b).

Habitat:— Stream and river banks frequently subjected to inundation, ca. 850 m.

Uses:— Cultivated as an ornamental following introduction to Australia in the 1980s ( Dowe & Ferrero 2000b).

Vernacular names:— None recorded.

Conservation status:— Data Deficient (DD; Petoe et al. 2018).

Specimens examined:— INDONESIA. Papua Province: Idenburg River [Taritatu River], Araucaria Creek , 4 km SW of Bernhard camp, 850 m, 3°29’S, 139°6’E, March 1939, Brass 13700 (A!, L!); Same locality as preceding, 850 m, 3°29’S, 139°6’E, March 1939, Brass 13608 (A!, L!). CULTIVATED . UNITED STATES. Hawaiian Islands: Hawai’i, Floribunda Palms , November 2017, Baker et al. 1436 (K!) .

Notes:— Hydriastele rheophytica is restricted to riverbanks where it forms large clumps of pliable, somewhat leaning stems. Only one other member of the genus, H. simbiakii , has a similar habitat preference although that species belongs to the Nengella group. Hydriastele rheophytica is distinguished by its leaves with numerous thin and soft, linear leaflets, the basal ones of which are obliquely praemorse at their tips, and a terminal leaflet pair comprising 2 or 3 folds. This species is most similar to H. variabilis , but that species has erect, non-pliable stems and terminal leaflets comprising 4–11 folds and it is not rheophytic.

A Brass photo showing H. rheophytica in its native habitat was reproduced in Rheophytes of the World ( van

Steenis 1981). The species is described in more detail by Dowe & Ferrero (2000b) and Petoe et al. (2018).

NENGELLA GROUP

Small to moderate palms, inflorescences protandrous and branched to 0 (spicate) or 1 order, triads spirally arranged (except in H. aprica where they are decussately arranged). New Guinea.

Figures

FIGURE 4. Distribution map of the species of the Wendlandiana group of Hydriastele.

FIGURE 10. Hydriastele rheophytica. A. Habit. B. Leaf apex. C. Mid-leaf portion. D. Leaf base. E. Infructescence. F. Portion of rachilla with pistillate flowers. G. Staminate flower whole and in longitudinal section. H. Pistillate flower whole and in longitudinal section. I. Fruit whole and in longitudinal section. Scale bar:A = 70 cm; B–D = 6 cm; E = 4 cm; F–G = 5 mm; H = 2.5 mm; I = 5 mm.A, I from Dowe 536; B–H from Brass 13700. Drawn by Lucy T. Smith.

FIGURE 11. Hydriastele rheophytica. A. Habit. B. Inflorescence and infructescences. C. Infructescence. All from Baker et al. 1436 (cultivated specimen).All photos: W.J. Baker.