Distinguishing features: Distinguished by the flat (not keeled) leaves with relatively short petioles and keeled leaflets with somewhat recurved margins. Leaf bases and trunks retain a dense dark brown tomentum that is not evident in other taxa from Arnhem Land, and the apical spine of the microsporophylls is more attenuate. Cataphylls are also short, soft and fleshy, but lack the dense orange tomentum seen in the closely related C. maconochiei. Three distinct populations occur, one on Groote Eylandt, another on the lower Blythe River in northern Arnhem Land, and another on the upper Goyder River in central Arnhem Land. These geographically separated populations are also morphologically distinct, and are here recognised as subspecies. Key to the subspecies. 1 leaflets 5.0--6.5 mm wide, 9--12 mm apart on rachis -- subsp. arnhemica 1* leaflets 3.5--5.5 mm wide, 6--8 mm apart on rachis 2 Male cones usually more than 8 cm diam., seeds usually more than 32 mm long -- subsp. muninga 2* Male cones usually less than 8 cm diam., seeds usually less than 32 mm long -- subsp. natja Cycas arnhemica subsp. arnhemica Illustration: Hill 1996, fig. 1. Distinguished by the robust habit and the dark green leaves with relatively short petioles and well-spaced, keeled leaflets with somewhat recurved margins. The leaflets are also distinctly angled towards the leaf apex, whereas those of subspp. muninga and natja are more or less perpendicular to the rachis. Distribution: locally abundant on deep white to yellow sands over laterites, in Eucalyptus tetrodonta - E. miniata dominated savanna forests around the Goyder River. Plants from farther north-east (around Badalngarrmirri Creek) show glossier, paler green leaves, leaflets with a more prominent midrib on the upper surface, and a more slender habit, suggesting some intergradation with C. orientis. Those from farther north-west, between the Blyth and Goyder Rivers, show smaller leaves with narrower and more crowded leaflets, indicating possible intergradation with subsp. natja, which occurs on the north coast of Arnhem Land. Conservation status: locally abundant in very remote country, not considered to be at risk. Cycas arnhemica subsp. muninga Illustration: Hill 1996, fig. 20. Distinguished by the crowded and numerous green leaves with crowded, relatively short, narrow leaflets with recurved margins. Subsp. arnhemica from central Arnhem Land differs in the larger leaves with longer, wider and more widely spaced leaflets. Subsp. natja from northern Arnhem Land is distinguished by its smaller cones and seeds. Distribution: known only from Groote Eylandt, mainly on old beach dunes in near-coastal sites. Conservation status: locally abundant, not considered to be at risk. Etymology: the epithet is a rendering of the name for this plant in the Anindilyakwa language of the aboriginal people of Groote Eylandt. Cycas arnhemica subsp. natja Illustration: Hill 1996, fig. 21. Distinguished by the crowded and numerous green leaves with crowded, narrow leaflets with recurved margins. Separated from subsp. muninga by the smaller cones and seeds. Specimens from Elcho Island are slightly larger in most respects, but still do not approach subsp. muninga in size of cones and seeds. Subsp. arnhemica from central Arnhem Land differs in the larger leaves with longer, wider and more widely spaced leaflets. Distribution: known from a small area along the north coast of Arnhem Land, apparently only on the lower Blyth River on the mainland, extending to Elcho Island. Intergradation with C. arnhemica occurs more inland, between the Blyth and Goyder Rivers (cited under C. arnhemica). Conservation status: locally abundant, not considered to be at risk. Etymology: the epithet is a rendering of the name for this species in the Burarra language of the local aboriginal people.
Description:
Stems arborescent, to 1.5(-2.5) m tall, 12-20 cm diam. at narrowest point. Leaves bright green to deep green, semiglossy, 70-160 cm long, flat (not keeled) in section (opposing leaflets inserted at 150-180° on rachis), with 160-260 leaflets, with white and orange or brown tomentum shedding as leaf expands or persistent below; rachis consistently terminated by a spine. Petiole 12-35 cm long, pubescent, unarmed or spinescent for 0-50% of length. Basal leaflets gradually reducing to spines. Median leaflets simple, strongly discolorous, 55-190 mm long, 3-6.5 mm wide, inserted at 60-90° to rachis, decurrent for 1-3 mm, narrowed to 2.5-5 mm at base (to 65-80% of maximum width), 4-14 mm apart on rachis; median leaflets section flat, or slightly keeled; margins recurved; apex acute or aristate, spinescent; midrib flat above, raised below. Cataphylls linear, soft, pilose, persistent. Pollen cones narrowly ovoid, orange, 18-36 cm long, 6.5-12 cm diam.; microsporophyll lamina firm, not dorsiventrally thickened, 20-30 mm long, 6-17 mm wide, fertile zone 15-22 mm long, sterile apex 6-9 mm long, level, apical spine prominent, sharply upturned, 5-14 mm long. Megasporophylls 15-24 cm long, grey-tomentose and brown-tomentose; ovules 2-6, glabrous; lamina lanceolate, 30-70 mm long, 14-22 mm wide, regularly dentate, with 18-26 pungent lateral spines 1-3 mm long, 1 mm wide, apical spine distinct from lateral spines, 8 mm long. Seeds flattened-ovoid, 28-32 mm long, 25-29 mm wide; sarcotesta orange-brown, not pruinose or slightly pruinose, 1.5-3 mm thick; fibrous layer absent; sclerotesta smooth. Spongy endocarp absent.
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