Areca unipa Heatubun, 2013

Heatubun, Charlie D., Iwanggin, Marthinus P. & Simbiak, Victor I., 2013, A new species of betel nut palm (Areca: Arecaceae) from western New Guinea, Phytotaxa 154 (1), pp. 59-64 : 59-63

Areca unipa Heatubun , sp. nov.

Type: — INDONESIA. West Papua Province: Maybrat Regency, East Aifat District, Ayata village , PT. Bima Cakrawala Nusantara Mining Concession Area , 200 m elev., 1°17’08.66” S, 132°37’28.02”, 17 July 2011, Iwanggin & Simbiak 138 (holotype MAN!, isotype K!) .

Diagnosis:— This new species is similar to Areca catechu L. and Areca mandacanii Heatubun in habit and inflorescence structure, but differs by having fewer leaves in the crown, by the slender leaf rachis and relatively long petiole, and the sigmoid multifold leaflets and broadly wedge-shaped terminal leaflets.

Solitary, slender palm tall up to 12 m high. Stem ca. 7.5 cm diam.; internodes 3–16 cm long, leaf scars 1–1.5 cm wide, not conspicuous, green near crown and dark to brownish grey near the base. Leaves 7 in crown, pinnate, ca. 119 cm long (including petiole); sheath tubular, ca. 54 cm long and ca. 7 cm wide, smooth, not fibrous, shiny cream to light green become dull green; crownshaft well defined, up to 75 cm long and up to 7 cm diam.; petiole ca. 16.5 cm long, slightly channelled adaxially, rounded abaxially; rachis slender, ascending but not arching, with adaxial longitudinal ridge, rounded abaxially; 9−10 leaflets on each side, more or less regularly arranged, spaced by 9–15 cm, basal leaflets ca. 42 × 1−4 cm, with 3 folds, sigmoid, middle leaflets 41−44 cm long, 1.5−2.5 cm wide at base and 7.5–11 cm wide at the tip, with 5 folds, sigmoid, terminal leaflet pair 14 cm long, 2–4 cm wide at the base and 4–7 cm at the tip, with 3–6 folds, broadly wedge-shaped to slightly cuneate, notched tips, the second and third leaflet pairs below the terminal pair splitting between the folds to about half way to the base, papery, discolorous, darker adaxially than abaxially. Inflorescence infrafoliar, slender, 30−40 cm long and 10−15 cm wide, protandrous, branching to 2 orders; prophyll elongated, slender, up to ca. 26 × 2 cm (very young stage), two-keeled, leathery, cream, light green near the apex; peduncle 1−4.5 cm long, green with numerous stellate hairs; rachis cream to yellowish green with thick rusty brown indumentum of stellate hairs; rachis bracts caducous; rachillae up to 21 cm long and 1−4 mm wide, slender, pale green, elongate and sinuous near the base; floral clusters distichous on rachillae, only one complete triad including female flower occurring at the base of each rachilla, remaining clusters comprising very few paired and solitary staminate flowers. Staminate flowers small, sessile, triangular, elongate or teardrop shaped, 4.5–6 × 2.1–2.5 mm in bud, asymmetric; sepals 3, low, ca. 2.1–2.5 × 1.1–1.5 mm, united at the base; petals 3, triangular, elongate or spathulate, 4.2–5 × 2.1–3.5 mm, striate; stamens 6, small, 2.2–2.8 mm long and 1 mm wide; filaments thick, 0.9 mm long and 0.1–0.4 mm wide, darker than anther; anthers ca. 2.2 mm long and 0.6 mm wide, sagittate, longer than the filaments; pistillode longer than stamens, 2.5–3.2 × 0.8– 1 mm, trifid. Pistillate flowers larger than the staminate, triangular, borne on the enlarged basal portion of rachillae, only one per rachillae, buds varying greatly in size depending on stage of development, 1.1 × 0.9 cm (in bud) to 2 × 1 cm (in late anthesis); sepals 3, strongly imbricate, ca. 1.5 × 0.9 mm in late anthesis, triangular, asymmetrical, striate; petals 3, imbricate, triangular, ca. 1.3 × 0.8 mm in late anthesis, striate; gynoecium 7–12 mm long and 3–5 mm; stigma ca. 3 mm long, pointed with 3 lobes, 0.3 mm long; style ca. 5–9 mm long; staminodal ring encircling gynoecium, 2 mm high, lacking differentiated staminodes. Fruit obovoid or ovoid with beak at the apex, 5.5−6 × 3.5−3.8 cm (unripe fruits), beak 4−6 mm long and 5–6 mm in diam.; epicarp smooth, shiny, dark green (unripe), mature fruits not seen; mesocarp fibrous, 0.5 cm thick, 1.5 cm thick at the base (below the seed); endocarp very thin, adhering closely to the seed. Seed obovoid, slightly flattened at base, ca. 3 × 2.2 cm (from unripe fruits); endosperm ruminate. Eophyl bifid. ( Figures 1 & 2 ).

Distribution: —Known only from the type locality in PT Bima Cakrawala Nusantara (a coal mining company) concession area, close to Ayata village in East Maybrat District, Maybrat Regency in the central part of the Bird’s Head Peninsula, West Papua Province, Indonesia.

Habitat: —This species grows in primary lowland peat forest at an elevation of about 200 m above sea level. It appears to be adapted to extreme conditions of the coal beds, which sometimes lack any apparent soil, except for leaf litter over the coal outcrop. Other palms observed growing in association with this new Areca include Calyptrocalyx sp. , several species of Hydriastele , Linospadix albertisianus (Becc.) Burret (1935: 331) , Licuala beccariana Furtado (1940: 37) , Licuala bifida Heatubun & Barfod (2008: 431) and Sommieria leucophylla Beccari (1877: 67) .

Local names: — Srah Owei Knu in (Aifat dialect, Mai Brat language). When the seedlings were planted in the nursery of the University campus in Manokwari, they were nicknamed pinang unipa (i.e. the betel nut of Universitas Papua).

Uses: —The fruits are chewed as a betel nut substitute. However, the palm has potential as an ornamental.

Conservation status: ––Critically Endangered CR B2ab (ii,iii,v), C1, E ( IUCN 2012). This palm meets the criteria for the extinction risk category Critically Endangered ( IUCN 2012) because its area of occupancy is estimated to be less than 10 km 2 and it is known to exist only in one population in a single locality. Habitat loss from both coal mining and oil palm plantation were identified as the major threat not only for this new species but also to the other plants in the region. It is projected that the area of occupancy, the area, extent and quality of habitat and the number of mature individuals will decline due to the coal mining activities. In addition, population size is estimated to number less than 250 mature palms. Plants occur at low density, with only two mature individuals found within a 10 ha plot. We also believe that the population will decline due to traditional harvesting by local people for the fruits as betel nut substitute, which they collect by chopping down mature individuals. The combination of threats faced by this very rare species strongly support our assessment of Critically Endangered.

Etymology: —The specific epithet refers to the acronym of Universitas Papua (the State University of Papua —UNIPA). This new species is named in celebration of the 10 th anniversary of Universitas Papua and formalizes its nickname “ pinang unipa ”.

Discussion: ––Prior to the discovery of this new taxon, three species of Areca were known from New Guinea (Heatubun, 2008; Heatubun et al. 2012). The most widespread species, A. macrocalyx Zipp. ex Blume (1839: 75) , is highly variable and some forms are superficially similar to A. unipa in vegetative morphology. However, A. macrocalyx has highly distinctive reproductive structures that are quite unlike A. unipa . Its inflorescence is protogynous, branched to one order (rarely two orders) and bears numerous (up to 600), closely spaced, slender, sinuous rachillae. Pistillate flowers occur only at the very base of the rachillae, the remaining portion bearing purely staminate flowers and drying and falling after anthesis. The maturing infructescence becomes congested with fruit, appearing spicate or club-like. None of these features correspond with A. unipa .

Areca unipa is most similar to A. catechu Linnaeus (1753: 1189) and A. mandacanii Heatubun (2008: 199) in its solitary, moderate tree palm habit and inflorescence structure, but it can immediately be distinguished by the small, slender leaves with relatively long petiole and very few multifold, sigmoid and broadly wedge-shaped leaflets. In contrast, A. catechu bears larger leaves with petiole short or almost lacking and single and/or multi-fold, linear leaflets, while A. mandacanii bears single-fold, linear leaflets that are arranged irregularly in groups and in several ranks. Besides that, this new species is smaller in almost all dimensions than A. catechu and A. mandacanii . For instance, A. unipa has seven leaves in the crown, a leaf about 102 cm long, 9–10 leaflets on each side of rachis, and inflorescence that is 30–40 cm long and branched to 2 orders. Areca catechu has 8–12 leaves in the crown, the leaf is 150–270 cm long with 20–35 leaflets on each side of rachis, and the inflorescence is 29–80 cm long and branched to 2–3 orders. Areca mandacanii has 8 leaves in the crown, the leaf is 200–250 cm long with about 60 leaflets each side of rachis, and the inflorescence is about 60 cm long and mostly branched to 2 (rarely 3) orders.

Though distinct, A. unipa , like A. mandacanii , is closely related to A. catechu , in its inflorescence architecture (divaricate panicle inflorescence with elongated branches and rachillae), the distichous floral clusters with only complete triad including female flower occuring at the base of each rachilla, the free sepals of staminate flowers (or sometimes fused at the base), six stamens and typical betel nut-like fruits. The discovery of yet another relative of A. catechu draws further attention to New Guinea as a potential area of origin for A. catechu as already highlighted by Heatubun et al. (2012). It is of great concern that this wild relative of an important crop species is so intensely threatened in its natural habitat.

Figures

FIGURE 1. Areca unipa. A. Habit. B. Apical portion of leaf. C. Middle and basal portion of leaf. D. Half portion of inflorescence. E. Staminate flowers on rachilla. F, G. Staminate flower whole and in section. H, I. Pistillate flower whole and in section. J. Detail of ovary and staminodal ring. K. Fruit. Scale bar: A = 75 cm; B, C = 8 cm; D = 4 cm; E, J = 7 mm; F, G = 2.5 mm; H, I = 1 cm; K = 3 cm. All from Iwanggin & Simbiak 138. Drawn by Lucy T. Smith.

FIGURE 2. Areca unipa. A. Slender habit with long petioled leaves and the sigmoid multifold leaflets and broadly wedge-shaped terminal leaflets. B. Inflorescence starting to expand after the prophyll has fallen off. C. Infructescence with several young fruits. All photos were taken from the holotype specimen (Iwanggin & Simbiak 138) in the forest near Ayata Village, East Maybrat, Maybrat, West Papua, Indonesia. All photos by Marthinus P. Iwanggin.