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Habit: dioecious fern-like shrubs with a naked often dichotomously branched subterranean stem. New leaves emerging singly. Cataphylls absent.
Leaves: pinnate, longitudinal ptyxis involute, horizontal ptyxis involute. Leaflets with circinate ptyxis and often a true terminal leaflet, lower leaflets not reduced to spines. Petioles lacking spines or prickles. Leaflets flat, penniveined, with a large midrib and numerous subparallel, bifurcating lateral veins and stomata on both surfaces. Leaves pubescent, at least when young, with coloured or transparent, unbranched trichomes.
Microsporophylls: spirally orthostichous, aggregated into stalked, ovoid male cones and each with a simple, flattened, broadly triangular, upturned and overlapping sterile apex. Each microsporophyll bearing numerous microsporangia (pollen-sacs) on the undersurface. Microsporangia opening by slits. Pollen cymbiform, monosulcate.
Megasporophylls: spirally orthostichous, aggregated into stalked, ovoid female cones. Sporophylls simple, with a broadly flattened, upturned sterile apex. Ovules two (rarely three), sessile, orthotropous, inserted on the inner (axisfacing) surface of the thickened lamina and directed inwards ("inverted"). Sporophylls in about 8 ranks, the expanded ends overlapping.
Seeds: subglobular to ellipsoidal, with a dark red sarcotesta. Endosperm haploid, derived from the female gametophyte. Embryo straight; with 2 cotyledons that are usually united at the tips and a very long, spirally twisted suspensor. Seeds radiospermic; germination cryptocotular.
| The Cycad Pages © 1998 Royal Botanic Gardens Sydney Written and maintained by Ken Hill Please send comments and corrections |