|The Cycad Pages
- Cycas armstrongii Miq., Arch. Néerl. Sci. Exact. Nat. 3(5): 235-236 (1868).
- "TYPE: Australia, Port Essington, Armstrong 380 (holo U; iso K)."
Honouring John Armstrong, a collector for Kew Gardens appointed
to establish a government garden at Port Essington in 1838.
Hill 1996, fig. 17.
[C. media forma inermis
Miq., Arch. Néerl. Sci. Exact. Nat. 3(5): 235 (1868), in
syn. (although Miquel refers to previous publications of forma
inermis (Miquel 1842: 7, 17; 1847: 412), this combination
was not actually published in these papers, he merely discussed
the unusual thornless specimen).]
distinguished by the glossy green mature new growth
and the discolorous leaflets with the midrib equally prominent above
and below. This species also has the smallest overall stature
of all Australian taxa. Originally distinguished on the basis
of the thornless petiole, but petioles are frequently at least
partly spinose, and wholly unarmed only on about 10--15% of individuals
in a population. This contrasts with C. conferta, which
has unarmed petioles in about 90% of individuals in a population.
The holotype specimen does not have a complete petiole, but Armstrong
379 does. The petiole of the latter is unarmed, and about
35 cm long, which is outside the usual range for C. armstrongii.
The leaflets, however, are well-spaced and match C. armstrongii
rather than C. conferta (the spacing is 10--12 mm, whereas
that of C. conferta is usually less than 8 mm).
Distribution and habitat:
an abundant species, in dense and extensive
populations on sand over Tertiary laterites in Eucalyptus miniata
- E. tetrodonta forests around Darwin. It extends from
the Adelaide River west to the Finniss River and south to the
township of Adelaide River, with sporadic occurrences farther
south almost to Hayes Creek and in a limited area on Melville
Island. Intergrading populations with C. conferta occur
at Mt Bundey and near Hayes Creek, and apparent hybrids are known
with C. maconochiei subsp. maconochiei.
This species is facultatively deciduous late in the dry season
of the monsoonal climatic cycle experienced in its natural habitat.
Plants in cultivation or in locally wetter sites can retain leaves
for longer, but become dormant, and it appears that the strong
seasonal stress is required to rejuvenate plants. Regular (almost
annual) dry-season fires experienced over much of the range also
promote leaf-drop, and fertile plants are frequently seen with
reproductive structure only, and no leaves. The regular fires
can also kill the above-ground parts of shorter plants, promoting
below-ground branching from an often massive swollen subterranean
The type was cited as `In Nova Hollandia
boreali ad portum Essington legit Armstrong n. 380 herb. Hookeri.'
John Armstrong was a collector for Kew Gardens appointed to establish
a government garden at Port Essington in 1838. He then collected
in Timor in 1839--45. His collecting ranged beyond the immediate
environment of the Port Essington settlement, a number of the
plants he collected not being known from that site (including Cycas
spp.). C. armstrongii has a limited natural distribution,
occurring only in the Darwin district, and the type must have
originated from there, considerably to the west of the Port Essington
settlement site. Three sheets are present in K, one labelled `No.
379/ Coll. in April 1839 at Port Essington', another labelled
`Port Essington/ Australia/ Armstrong', and the third labelled
`Port Essington/ (bis)'. The U specimen consists of two leaflets
only, but with the rachis cut to match the second of the above
K sheets. It appears that the second and third K sheets and the
U sheet are all parts of Armstrong 380, and consequently
parts of the holotype. Bentham (1873) included C. armstrongii
in C. media, and his treatment was followed until Maconochie
(1980) recognised the distinctive nature of C. armstrongii,
although not on the basis of the unarmed petiole as Miquel had
done originally (see below). Although Miquel in the protologue
referred to previous publications of forma inermis (Miquel
1842: 7, 17; 1847: 412), this combination was not actually published
in these papers, he merely discussed the unusual thornless specimen.
This is also an indication that Miquel had seen more than just
the U specimen, which has no petiole.
locally extremely abundant, not considered
to be at risk. Although not well reserved, the extreme abundance
of this species would buffer it from any threat in the medium
term. However, frequent fire effectively blocks reproduction,
and uncontrolled development progressively alienates significant
proportions of the habitat. Several of the Northern Territory
species, including this one, are probably the most abundant of
all cycads, with populations numbering into tens of millions.
Stems arborescent, to 3(-6) m tall, 5-11 cm diam. at narrowest point.
Leaves bright green, semiglossy to highly glossy, 55-90 cm long, slightly keeled to flat (not keeled) in section (opposing leaflets inserted at 130-160° on rachis), with 100-220 leaflets, with white and orange tomentum shedding as leaf expands; rachis usually terminated by a spine. Petiole 10-25(-35) cm long, glabrous, spinescent (usually), for 20-60% of length. Basal leaflets not gradually reducing to spines.
Median leaflets simple, weakly discolorous, 55-140 mm long, 4.5-8 mm wide, inserted at 70-90° to rachis, decurrent for 3-5 mm, narrowed to 3.5-5 mm at base (to 50-85% of maximum width), 6-14 mm apart on rachis; median leaflets section flat; margins flat; apex aristate, not spinescent; midrib raised above, raised below.
Cataphylls linear, pungent, pilose, persistent.
Pollen cones ovoid, orange, 11-20 cm long, 7.5-10 cm diam.; microsporophyll lamina firm, not dorsiventrally thickened, 25-35 mm long, 14-17 mm wide, fertile zone 24-28 mm long, sterile apex 4-6 mm long, level, apical spine prominent, sharply upturned, 7-10 mm long.
Megasporophylls 13-22 cm long, grey-tomentose and brown-tomentose; ovules 2-4, glabrous; lamina lanceolate, 30-70 mm long, 18-35 mm wide, regularly dentate, with 20-28 pungent lateral spines 1-4 mm long, 1-2 mm wide, apical spine distinct from lateral spines, 10-25 mm long.
Seeds flattened-ovoid, 34-37 mm long, 32-36 mm wide; sarcotesta orange-brown, not pruinose, 3-4 mm thick; fibrous layer absent; sclerotesta smooth. Spongy endocarp absent.