Arenga talamauensis Mogea 2004

Abstract

1.20. Arenga talamauensis Mogea (2004: 187). Type:— INDONESIA, Sumatra, Prov. West Sumatra, District Pasaman, Lubuk Sikaping, Bukit Kabung, primary dipterocarp forest, 800–1000 m, 22 June 1907, Bünnemeijer 1216 (holotype BO!). Stems clustered, number of stems per cluster not recorded, ca. 20 cm long, 0.2 cm diameter at the base; internodes not recorded; periderm not recorded. Leaves number per stem not recorded, paripinnate or imparipinnate, 40–160 by 25– 35 cm, distribution along the stems not recorded, erect; leaf sheaths 20 cm long, diameter not recorded, disintegrating in a brown fibrous mat; ligules to 1cm long; petioles slender, (3)12–16 by 0.3 cm, rounded in cross section, covered with dense light brown indumentum; rachises 30–45 cm long, 0.3 cm wide at the base; petiolules absent or to 1 cm long; pinnae 4 per side of the rachis, 16–18 by 6–8 cm, trullate, regularly arranged along the rachis, horizontally spreading, ± in 1 plane, adaxial surfaces color not recorded, abaxial surfaces light white-silvery, margins of the top part of the pinna praemorse and densely toothed, teeth to 1 mm long, slightly to conspicuously acuminate, acumen to 1cm long; apical pinna obtriangular, asymmetric, 12–14 by 3.5–7 cm. Inflorescences unisexual, multiple, pendulous, developing in a basipetal direction, to 35 cm long, branched to 1 order; staminate inflorescence axillary, developed along a long inflorescence axis, 15–35 by 7–15 cm; prophylls tube–like, ca. 2 cm long; bracts 4, tattered, the young bracts tube–like, 12–15 cm long; peduncles 5–7 by 0.2–0.3 cm, rounded in cross section, arching downwards; rachillae to 5, 12–20– 0.1 cm, rounded in cross section, color not recorded, glabrous; staminate flowers in dyads but apparently only one out of the two developed to anthesis, spirally arranged along the rachillae, ellipsoid in bud, 6–7 by 3–4 mm; sepal 3, imbricate, ellipsoid, 1.5–2 by 3–3.2 mm, margins entire or with 1–2 superficial notches to 0.3 mm long, outside surfaces color not recorded, surfaces glabrous; petals 3, valvate in bud, ellipsoid, 6–9.5 by 2–3 mm, coriaceous, outside surfaces color not recorded; stamens 15–25; filaments slender, 2–5 by 0.1 mm; anthers 2–3 by 0.8–1 mm, not aristate; pistillate inflorescence similar to staminate ones, usually at the 3rd or 4th lower nodes of the inflorescence axis; pistillate flowers possibly solitary, spirally arranged along the rachillae, ellipsoid, ca. 4 by 3 mm; sepal 3, imbricate, ellipsoid, ca. 3 by 2.5 mm, ovate ca. 3 mm long, margins not recorded, color of outside surfaces not recorded; petals 3, valvate in bud, ellipsoid, ca. 6 by 2 mm long; staminodes absent; gynoecia globose, ca. 2.5 mm diameter; locules not recorded; stigmas 2, sessile, ca. 0.8 mm long; fruits (only known from one apparently immature fruit from De Wilde 16625) 1-seeded, globose, ca. 6–7 mm diameter, color not recorded; stigmatic remains apical, to ca. 1 mm long; seeds (immature) globose; testa not recorded; hilum not recorded, 4.5 mm diameter; endosperm not recorded, embryos not recorded. Eophylls not recorded. Distribution and habitat:— Sumatra (Aceh, West Sumatra) (Fig. 25) in primary dipterocarp forests and montane rainforests at 800–1400 m elevation. Notes:— Mogea (2004) considered Arenga talamauensis to have paripinnate leaves, but this may not always be the case. The species is known from two specimens. The type specimen comprises two leaves with a bifid apical pinna. The other specimen (de Wilde 16625) consists of a paripinnate leaf. Another possibility would be that de Wilde 16625 does not represent A. talamauensis, and in this case that the specimen potentially represents a new species. More collections of A. talamauensis are urgently needed. Reproductive biology:— Arenga talamauensis is hapaxanthic with a basipetal inflorescence development. Many data are still missing concerning this species. One possible scenario is that at sexual maturity a long inflorescence axis is produced in continuation with the short stem (in apical or axillary position). From this long, slender axis several multiple inflorescences develop in a basipetal direction. Other inflorescence axes develop beside this “terminal one”. This organization of the different inflorescences in condensate structures appears comparable to what happens in some individuals of Arenga caudata, A. nana and Caryota monostachya. If, as Mogea (2004) stated, all the inflorescences appear along this inflorescence axis and the apical ones are all staminate while the proximal ones are pistillate, this would be the first time such a spatial sexual arrangement is observed in the Caryoteae. Etymology:— talamauensis, in reference to Mount Talamau, one of the localities where this palm was collected. Preliminary IUCN conservation status:—Critically Endangered [CR] – Arenga talamausensis is endemic to Sumatra. Its Extent of Occurrence (EOO) is 0 km 2 (below the 100 km 2 upper limit for Critically Endangered status under the criterion B1) and its area of occupancy AOO is estimated to be 8 km 2 (below the limits for Critically Endangered status under the criterion B2). The species is known from 3 “locations” (sensu IUCN 2012), exceeding the upper limit of the Critically Endangered status. Very little is known about this species throughout its range, and an important decline of its EOO and AOO can be predicted due to the important deforestation currently going on in Sumatra. Since the conditions for applying subcriteria a under criterion B1 and B2 are met, and considering the destruction of its habitat, the species is thus assigned a preliminary status of CR. In the event that Arenga talamauensis should be proved more abundant due to a better collecting effort, the present conservation status would be revised. Additional specimens examined:— SUMATRA. Sumatera Barat, Talamau. Apr 1917 (fl), Bünnemeyer, H. A. B. 473 (BO!); Aceh, Mamas, 6 May 1975 (fl), Wilde, W. J. J. O. de 16625 (K!).

Authors 3

1. Marc L. Jeanson

   Muséum national d'Histoire naturelle · Institut de Systématique, Évolution, Biodiversité · New York Botanical Garden

   Affiliation as printed

   Center for Biodiversity & Evolution, The New York Botanical Garden, Bronx, NY 10458 - 5126, U. S. A. & Muséum National d'Histoire Naturelle, Département Systématique et Evolution, UMR 7205 Origine Structure et Evolution de la Biodiversité, 16 Rue Buffon, 75231 Paris cedex 05

2. Thomas L. P. Couvreur Aachen Botany Section

   Institut de Recherche pour le Développement · Université de Montpellier · Centre de Coopération Internationale en Recherche Agronomique pour le Développement · Diversité, adaptation et développement des plantes · Naturalis Biodiversity Center

   Affiliation as printed

   DIADE, Univ Montpellier, IRD, CIRAD, Montpellier, France https: // orcid. org / 0000 - 0002 - 8509 - 6587 & Naturalis Biodiversity Centre, Botany Section, Darwinweg 2, 2333 CR Leiden, The Netherlands

3. Andrew Henderson

   New York Botanical Garden

   Affiliation as printed

   Center for Biodiversity & Evolution, The New York Botanical Garden, Bronx, NY 10458 - 5126, U. S. A. & Center for Biodiversity & Evolution, The New York Botanical Garden, Bronx, NY 10458 - 5126, U. S. A. ahenderson @ nybg. org; https: // orcid. org / 0000 - 0001 - 6334 - 9435 & Center for Biodiversity & Evolution, The New York Botanical Garden, Bronx, NY 10458 - 5126, U. S. A