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For many years relative to plant studies in our so called Top End, there have been reports of a slender trunked form of Cycas with pronounced silver colouration through the young upright fronds. Great fields of these grow amongst the rocks of limestone outcrops and show the first return to colour in areas annually burned off by aboriginals.
Maconochie, the Northern Territory botanist, was dedicated to the study of the genus Cycas and indeed is credited with the descriptions of two species during the 1970s period; Cycas pruinosa and C. calcicola, the species in question.
J.R. Maconochie describes this Cycas in his official papers released during 1978 by the Herbarium of the Northern Territory, Dept. of the Northern Territory, Alice Springs. His listed habitats at that period were always in or near limestone outcrops and in open forest in areas just north of Katherine. Two other populations mentioned being at Bamboo Creek on the Mandora Road south of Darwin and the other on the East Alligator River. Further to this comes reports of finding colonies in the Finniss River area by a young naturalist with all the keen dedication of the late J.R. Maconochie. Don Stallard of Darwin has even had success in getting some Cycas species placed on the 'Trees of Significance' listing. Don is convinced of the possible hybridization in nature of Cycas calcicola and C. armstrongii.
It is now evident that the two species spill into each other's territory in the Top End, and Don is convinced that hybrids exist between these species. So far he has found the overlap in the Florence Falls area and north of Katherine and upper reaches of the Daly River.
The following description is from J.R. Maconochie (1977) Palm-like shrub to 3 m high, trunk about 17-30cm diameter. Fronds dark-green, flattened or arcuate in cross section, (60-)80-90(-115)cm long, (9-)15-20 (-27)cm wide. Leaflets or pinhas (150-)200-280 (-300) in number with revolute margins, glabrous or pubescent above, pubescent in channels below. Pinnae 8-12cm long, 2.5-3m m occasionally 4mm wide, straight to slightly curved, apex attenuate to mucronate with a small spine I mm long, slightly angled on the rachis, not decurrent on the rachis. Rachis (including petiole) round to tetragonal towards the base, about 10mm wide and 8mm thick at base to 2mm wide near tip, glabrous scurfy-ferruginous. Male cone narrow ovoid, 17-26cm long and 5-6cm wide, microsporophyll deltoid 15-25mm long, 5mm and 12mm wide at base and apex respectively, with the terminal portion 6-10mm long, grey-pubescent with a hooked tip in the same plane. Megasporophyll ferruginous to 15cm long, with elliptic-rhombic sterile apex and a weakly developed spine 10-16mm long. Sterile apical regions 20-25mm long, 1-1lmm broad with 7-8 fine papery marginal teeth or entire, lower surface ferruginous-pubescent, upper surface glabrous with a mottled brown-green papery or dried resinous surface. Megaspores 2 to 6 per sporophyll, globular-ovoid, brown in colour, surface slightly glaucous, about 32-35mm long and 25-27mm in diameter.
Len Butt (Text and Figure 1)(from Palms & Cycads No. 27, Apr-Jun 1990)
Gary Beaumont (Figure 2,3,4,5,6)