Tahina spectabilis J.Dransf. & Rakotoarin., Bot. J. Linn. Soc. 156: 84 (2008)

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Content

Distribution

Map uses TDWG level 3 distributions (https://github.com/tdwg/wgsrpd)
Madagascar present (Dransfield, J., Rakotoarinivo, M., Baker, W.J., Bayton, R.P., Fisher, J.B., Horn, J.W., Leroy, B. & Metz, X. 2008: A new Coryphoid palm genus from Madagascar)A
Tahina spectabilis is known only from one locality in Analalava district, in the north-west of Madagascar. In the gently rolling hills and flatlands of the region, now dominated by anthropogenic grasslands, there is a small outcrop of "tsingy". karst Tertiary limestone, running approximately north-south and about 250 m long, carrying a semi-natural vegetation (Fig. 3A). The outcrop is visible in satellite imagery at Google Earth and the grey crowns of the palm are even visible, although blurred. (Dransfield, J., Rakotoarinivo, M., Baker, W.J., Bayton, R.P., Fisher, J.B., Horn, J.W., Leroy, B. & Metz, X. 2008: A new Coryphoid palm genus from Madagascar)A

Diagnosis

  • Palma solitaria grandis hapaxantha ad 10 m alta, tronco ad 50 diametro; inflorescentia terminalis composita ad 4 m alta; fructus ad 3.5 x 2.7 cm, endospermio ruminato. (Dransfield, J., Rakotoarinivo, M., Baker, W.J., Bayton, R.P., Fisher, J.B., Horn, J.W., Leroy, B. & Metz, X. 2008: A new Coryphoid palm genus from Madagascar)A

Biology And Ecology

  • Although the annual precipitation is estimated to be about 1600 mm, the climate of this locality is classed as dry and warm. Drought is manifest because of the eight dry months, the mean annual temperature around 27 °C, and the very strong insolation throughout the year (source: Bioclim, 2006; http://www.bioclim.org). Moreover, the high permeability of the limestone may also decrease the moisture rate during the warmest period of the day. At the same time, edaphic conditions in the tsingy are harsh; soil scarcely exists in many places, and leaf litter is always thin and poorly decomposed. The vegetation is a low woodland dominated by xerophytes and succulents, such as species of Euphorbia, Aloe, and Kalanchoe. About 90 individuals were seen, most of them growing on the sandstone plain at the edge of the tsingy, and a single, short individual was also found near the village of Antsanifera. The sandstone plain is covered by herbaceous savannah with abundant individuals of the palm Hyphaene coriacea, and environmental conditions are totally different. The humidity rate is much higher as water stagnates during the humid season. Individuals of T. spectabilis on these flats are robust and often occur in groups of two to five trunks. The individual sampled was on this plain. Analysis of the potential distribution of T. spectabilis using Maxent 2.2 identified only the coastal region of the north-west, between Analalava and Mitsinjo (Fig. 4), as a suitable habitat. This small predicted area can primarily be explained by the high sensibility of this palm to temperature variations during the coldest and driest season (June?September) as well as the geology type (Fig. 4; training gain, 2.7?3.2). The coastal region in which the palm is found is always much warmer than the adjacent inland area. Temperatures between June and September in the coastal region do not fall below a mean of 25 °C and a minimum of 19 °C, whereas those inland may decrease to 22 and 16 °C, respectively. These temperature differences over a small distance seem to be critical, and may inhibit the colonization of new areas. (Dransfield, J., Rakotoarinivo, M., Baker, W.J., Bayton, R.P., Fisher, J.B., Horn, J.W., Leroy, B. & Metz, X. 2008: A new Coryphoid palm genus from Madagascar)A

Description

  • Solitary tree palm, 4-10 m tall. STEM bulbous at the base, diameter at breast height 50 cm, internodes 8-10 cm, nodes 1.5-3.5 cm. LEAVES marcescent in young individuals, costapalmate, 12-18 in the adult crown, leaf sheath 80-100 x 52-58 cm, fibrous in the margin, petiole 3.50-3.80 m long, abaxially deeply channelled, margin smooth, proximal part 10.5-12 cm in diameter, distal part 6-8.5 cm in diameter, costa c. 1.60 m long, lamina 3.80-4.10 m in diameter, divided to c. one-half the radius into 110-122 induplicate segments, thinly covered with white tomentum on the abaxial surface, segment apices bifid. INFLORESCENCE terminal, compound, 4 m long, each lateral unit branched to three orders, 21 first order branches up to 2.50 m long, tubular bract 9-25 cm long, open at 6-9 cm in the distal part, covered with white caducous indumentum, rachillae 10-15 cm. FRUITS broadly ellipsoid to obovoid, 25-30 x 20-22 mm, borne on the stalk-like corolla base, 5-7 x 2 mm, perianth persistent, green yellowish at maturity, 3-3.5 cm long, 2.3-2.7 cm wide, stigmatic remaining apical, pericarp fleshy, endocarp 13-17 x 17-22 mm. SEED globose, 1.8-2.2 cm long, 1.4-1.8 cm wide, with anastomosing grooves, endosperm strongly ruminate. (Dransfield, J., Rakotoarinivo, M., Baker, W.J., Bayton, R.P., Fisher, J.B., Horn, J.W., Leroy, B. & Metz, X. 2008: A new Coryphoid palm genus from Madagascar)A

Relationships

  • The induplicate fan leaf clearly places Tahina in subfamily Coryphoideae. Within Coryphoideae, the syncarpous gynoecium is found in the clade that includes Chuniophoeniceae, Caryoteae, Corypheae, Sabaleae, and Borasseae (here termed the syncarpous clade, see Fig. 6). The Caryoteae have pinnate or doubly pinnate leaves and unisexual flowers arranged in triads. The Borasseae are all dioecious and have fruits with hard, sometimes ornamented, endocarps that usually have apical pores, and seeds with apical embryos. The Corypheae have hermaphroditic flowers arranged in cincinni subtended by minute incomplete rachilla bracts, and seeds with apical embryos. The strictly tubular imbricate rachilla bracts and pedicelliform corolla bases of the new palm are found only in tribe Chuniophoeniceae (Dransfield et al., 2005), a small well-supported tribe comprising three genera: Nannorrhops in Arabia, Iran, Afghanistan, and Pakistan; Kerriodoxa in southern Thailand; and Chuniophoenix in Vietnam, southern China, and Hainan. The three genera display unusual morphological diversity, particularly in vegetative characters, yet molecular evidence strongly supports their sister relationships. Nannorrhops (monotypic) is a shrubby clustering and dichotomously branching hapaxanthic palm of desert regions, with a leaf lacking a hastula; the large compound inflorescence is suprafoliar. Kerriodoxa (monotypic) is a relatively large, single-stemmed pleonanthic palm of the forest undergrowth with a single stem; it has a well-developed hastula and inflorescences are interfoliar. The two or three species of Chuniophoenix are either slender reed-like or moderate shrubby pleonanthic palms of forest undergrowth with clustering stems, leaves lacking hastulae, and interfoliar inflorescences. (Dransfield, J., Rakotoarinivo, M., Baker, W.J., Bayton, R.P., Fisher, J.B., Horn, J.W., Leroy, B. & Metz, X. 2008: A new Coryphoid palm genus from Madagascar)A

Bibliography

    A. Dransfield, J., Rakotoarinivo, M., Baker, W.J., Bayton, R.P., Fisher, J.B., Horn, J.W., Leroy, B. & Metz, X. 2008: A new Coryphoid palm genus from Madagascar