Etymology: Honouring French botanist Louis-Marie Aubert du Petit-Thouars (1758-1831). Literature: Stapf 1916, Prain 1917, Melville 1958, de Laubenfels 1972, Woltz 1967. Illustrations: Warburg 1900, Schuster 1932 (as C. circinalis ssp. madagascariensis), Melville 1958, de Laubenfels 1972. Historical notes: Madagascan cycads were first recorded under the name C. circinalis by Louis-Marie Aubert du Petit-Thouars in his review of the botany of French colonial possessions in the Indian Ocean in 1804. They were again discussed by Robert Brown in 1810 under the name C. thuarsii? (sic - with a query), with the observation that they scarcely differed from plants from India and Ceylon. He had apparently studied specimens at Kew that had been collected ?from Madagascar by du Petit-Thouars. Brown did not furnish a valid description, but it has been argued that his reference to du Petit-Thouars can be accepted as a basionym. C. thouarsii was again described in 1829 by French explorer and botanist C. Gaudichaud-Beaupre (1829), in his treatment of the botany in M.L. de Freycinet's account of voyage of the S.M. Uranie. He provided a minimal but valid description, and attributed the name to Robert Brown. No Type was cited. The name was attributed to Robert Brown ("Ex R. Brown"), and distribution cited was "In Insulâ Madagascar". However, Brown did not actually publish the name, but merely referred to collections by du Petit-Thouars from Madagascar and seen at K (du Petit-Thouars collections are mainly at P and PC, with some at K and BM). These collections would constitute the type. Miquel (1840, 1842, 1843) described the Madagascan cycad as a new species C. madagascariensis, apparently in ignorance of Gaudichaud's publication. He later (1861, 1868) accepted C. thouarsii and placed C. madagascariensis in synonymy, attributing the name to Brown. De Candolle (1868) followed Miquel, but regarding the species as dubiously distinct from C. rumphii. Braun (1886) also followed Miquel, accepting C. thouarsii as distinct from C. rumphii on the basis of seed size. French nurseryman and rare plant dealer G--- Bruant of Poitiers next introduced the name C. comorensis in his 1888 catalogue, but did not furnish a valid description. This was for plants he had grown from seeds collected in 1885 by --- --- and explorer --- Humblot in the Comoros. A large quantity of seeds was apparently imported into France from both Humblot and Hildebrandt, and distributed among a number of interested parties. Plants grown from these seeds made their way into horticulture under various names. Duchartre (1888) almost immediately afterwards discussed application of these names, and returned to C. thouarsii. Warburg (1900) distinguished C. thouarsii from both C. rumphii and C. circinalis on details of the microsporophylls. Engler (1908), however, reduced it to C. circinalis subsp. thouarsii. Stapf (1916) supplied detailed discussion of the nomenclature and specific limits, arguing that Brown's comments constituted a valid publication typified on the description and specimens of du Petit-Thouars. He concluded that close similarities existed with C. rumphii, but that botanical science would be better served by recognition of the two as distinct species. Despite the considerable discussion of the nomenclature and affinities of this species, Schuster (1932) placed it under C. circinalis as variety madagascariensis, based on Miquel's earlier name. Schuster had rejected Brown's publication as a nomen nudum, but had apparently overlooked Gaudichaud's valid publication of the name. Melville (1958) reinstated the name C. thouarsii, attributing it to Gaudichaud (1829). He was followed by de Laubenfels (1972). Distinguishing features: Distinguished within the group of species with spongy endocarp by the distinctly bluish new leaves with wholly spinescent petioles and the pronounced stout spines on the microsporophylls. Seeds do not have a crested sclerotests. Distribution and habitat: Like others in this grouop, C. thouarsii is a species of near-coastal sites, in forests behind beaches and on headlands, often on calcareous sand derived from corals. Abundant in Madagascar, particularly in east coast forests, also on the Comoro group. Scattered occurrences are known on the coast of East Africa from Tanzania (Pemba) south the Mozambique. These have been claimed to be introduced by man (Goode ), but some of the stands appear to be long-established and likely to pre-date seafaring traders. Conservation status: Abundant in some parts of Madagascar but unreserved and under some threat from habitat destruction. 1994 IUCN Red List of Threatened Plants category LR, cd.
Description:
Stems arborescent, to 4 m tall. Leaves deep green, semiglossy, 150-210 cm long, flat (not keeled) in section (opposing leaflets inserted at 170-180° on rachis), with 180-200 leaflets, tomentum shedding as leaf expands; rachis usually terminated by paired leaflets. Petiole 40-50 cm long, glabrous, spinescent for 70-90% of length. Basal leaflets not gradually reducing to spines, 170 mm long. Median leaflets simple, strongly discolorous, 220-320 mm long, 8-11 mm wide, inserted at 45° to rachis, decurrent for 4-7 mm, narrowed to 4-5 mm at base (to 45-55% of maximum width), 13-18 mm apart on rachis; median leaflets section flat; margins slightly recurved; apex acute, not spinescent; midrib raised above, raised below. Cataphylls narrowly triangular, pungent, pilose, persistent. Pollen cones fusiform, orange to brown (pale); microsporophyll lamina firm, not dorsiventrally thickened, apical spine prominent, sharply upturned. Megasporophylls 29-32 cm long, yellow-tomentose; ovules 2-6, glabrous; lamina ovate to lanceolate, 80-100 mm long, 20-25 mm wide, obscurely dentate, with 12-16 soft lateral spines 0-2 mm long, apical spine distinct from lateral spines, 15-35 mm long. Seeds ovoid, 50-60 mm long; sarcotesta orange-brown; fibrous layer absent; sclerotesta smooth. Spongy endocarp present.
|
