Etymology:
Honouring English botanist Sir William Turner Thiselton-Dyer (1843-1928), director of the Royal Botanic Gardens Kew (1885-1905).
Historical notes: Distinguishing features: Distinguished by the very robust and arborescent habit, the strongly keeled, dull leaves with relatively few leaflets, the broad leaflets, and the slender male cones with short apical spines on the sporophylls. Distribution and habitat: South-western Australia, from Monglinup River east to Israelite Bay. Locally abundant in coastal shrublands and heaths on deep calcareous beach sand deposits. Conservation status: Not considered to be at risk (IUCN Red List category LR,lc).
Description:
Plants arborescent, stem 0.4-3 m tall, 50-120 cm diam. Leaves 70-150 in crown, grey-green, semiglossy, 180-240 cm long, moderately keeled (opposing leaflets inserted at 90-120° on rachis), with 70-100 leaflets; rachis not spirally twisted, recurved, arching stiffly downwards; petiole 26-63 cm long, straight, spinescent; basal leaflets reducing to spines. Leaflets simple, weakly discolorous; margins flat; apex entire, spinescent; median leaflets 330-455 mm long, 12.5-17 mm wide. Pollen cones fusiform, 48-62 cm long, 10-14 cm diam.; microsporophyll lamina 32-44 mm long, 20-29 mm wide; apical spine 2-22 mm long. Seed cones narrowly ovoid, 45-50 cm long, 15-20 cm diam.; megasporophyll with an expanded peltate apex 50-60 mm wide, 30-40 mm high; apical spine 2-50 mm long. Seeds ovoid, 43-55 mm long, 28-36 mm wide; sarcotesta red.
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