 |
|
Habit: dioecious fern-like shrubs with a naked subterranean stem producing one to many short, slender, determinate leaf and conebearing branches, sometimes themselves branched. New leaves emerging singly. Cataphylls absent.
Leaves: bipinnate, longitudinal ptyxis circinate, 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, lacking a midrib, with numerous subparallel longitudinal veins and stomata on both surfaces, individual ptyxis flat. Leaves pubescent, at least when young, with coloured or transparent, unbranched hairs.
Microsporophylls: spirally orthostichous, aggregated into male cones and each with a simple, peltate sterile apex, which is not produced into a terminal spine. Each microsporophyll bearing numerous microsporangia (pollen-sacs) on the undersurface. Microsporangia opening by slits. Pollen cymbiform, monosulcate. Male cones stalked, ovoid.
Megasporophylls: spirally orthostichous, aggregated into female cones. Sporophylls simple, with a dilated peltate apex or lamina which is not produced into a terminal spine. Ovules two (rarely three), sessile, orthotropous, inserted on the inner (axisfacing) surface of the thickened lamina and directed inwards ("inverted"). Female cones stalked but not elevated above soil surface, ovoid to globose; sporophylls in about 8 ranks, the expanded ends hexagonal.
Seeds: subglobular to ovoid, with a white aging to purple 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 |