|Photo Ken Hill
|The Cycad Pages
- Cycas bougainvilleana K.D. Hill, "Austral. Syst. Bot. 7: 557-560, fig. 11." (1994). H—NSW
- "TYPE: Papua New Guinea, Bougainville District, Buin Subdistrict, Tonolei Harbour, C.D. Sayers NGF 19739, 26 June 1964 (holo NSW; iso A, BRI, CANB, LAE, K, L; label also records distribution to BO, PNH, SING, UH)."[NSW]
In reference to the centre of distribution and development of
this species on Bougainville Island.
Hill 1994c, fig. 11.
Recognised as a distinct taxon in 1994.
C. bougainvilleana is distinguished by the very broad,
falcate leaflets with a hard, glossy cuticle, continuous laminar
hypodermis and mesophyll interrupted by the broad, low midrib,
the relatively short, thick, usually partly spinescent petiole,
and the large, heavy, narrowly triangular megasporophyll lamina
with 16-32 lateral spines that are 4-9 mm long. It is nearest
to C. seemannii, differing in being generally more robust
in all features, together with the possession of continuous adaxial
hypodermis and a usually partly spinescent petiole. Cataphylls
are also longer and more pungent. This species reaches its best
development on Bougainville, being slightly less robust in the
New Britain Group. This is interpreted as a result of genetic
inflow from mainland New Guinea introducing a different
gene complement into New Britain, possibly from C. rumphii. Similar but
even more highly variable forms occur in the islands off the eastern
point of the New Guinea mainland (the Trobriand, D'Entrecasteax
and Louisiade groups), possibly representing a higher degree of mixing
and subsequent hybrid segregation of C. bougainvilleana
and C. scratchleyana. Plants from the Solomon Islands are
nearest to C. bougainvilleana, but are also very highly
variable, with the range also approaching C. seemannii.
Similarly, plants from Vanuatu are somewhat more robust than is
usual in C. seemannii, but less so than in the Solomoms.
There is also a suggestion that intergradation occurs with C.
rumphii sens. strict. to the west through the Admiralty group
(Manus Island) and the north-east coast of mainland New Guinea.
The variability in the Solomon Islands, Vanuatu and the Admiralty
Islands is interpreted as a product of genetic interchange resulting
from successive waves of colonisation facilitated by the aquatic
Distribution and habitat:
Confined to near-coastal sites in Bougainville, New Britain and
the Solomom Islands. Sporadic but locally abundant, on stabilised
calcareous coral-sand dune country and nearby headlands, often
in more or less closed mesophyll forest.
di di (Ambungi village, N. Brit.), diduna (Tonolei
village, N. Brit.), pago (Matong and Pomio villages, N. Brit.),
diriuna (Suvai village, Boug.), bai bai, bae bae (Rennel and Baga
Is., Solomon Is.)
|Photo Ken Hill
Stems arborescent, to 5 m tall.
Leaves bright green, highly glossy, 240-270 cm long, flat (not keeled) in section (opposing leaflets inserted at 180° on rachis), with 130-260 leaflets, tomentum shedding as leaf expands; terminated by a spine or paired leaflets; 3-11 mm long. Petiole 30-65 cm long, pubescent, unarmed or spinescent. Basal leaflets not gradually reducing to spines.
Median leaflets simple, strongly discolorous, 250-340 mm long, 13-18 mm wide, inserted at 60-80° to rachis; section flat; margins slightly recurved; not spinescent; midrib raised above, raised below.
Cataphylls linear, pungent, pilose, persistent.
Pollen cones fusiform, yellow to brown (pale); microsporophyll lamina firm, dorsiventrally thickened, apical spine rudimentary, sharply upturned.
Megasporophyll lamina ovate to lanceolate, 70 mm long, 35-50 mm wide, regularly dentate, with pungent lateral spines, apical spine distinct from lateral spines; ovules 4-10, glabrous.
Seeds flattened-ovoid; sarcotesta orange-brown; fibrous layer absent; sclerotesta apically crested. Spongy endocarp present.