A family with a single genus: Cycas Habit: dioecious palm like shrubs with aerial or subterranean, pachycaul, cylindrical stems. Leaves: pinnate, spirally arranged, produced in seasonal growth flushes interspersed with cataphylls, lower leaflets often reduced to spines. Longitudinal ptyxis erect or rarely reflexed, horizontal ptyxis circinate. Leaflets with a single thick midrib and no lateral veins; stomata confined to abaxial surface in most species; individual ptyxis involute. Leaves pubescent, at least when young, with branched or simple transparent trichomes. Microsporophylls: aggregated into determinate male cones and each with a simple sterile apex, which is often produced into an upturned spine. Each microsporophyll bearing numerous microsporangia (pollen sacs) on its abaxial surfaces. Microsporangia opening by slits. Pollen cymbiform, monosulcate. Megasporophylls: loosely or tightly imbricate, spirally arranged in an indeterminate terminal rosette with the central axis continuing vegetative growth. Ovules two to many (rarely one), marginally inserted on the stipe and directed obliquely outwards (`ascending'). Megasporophyll apically dilated into a pinnatifid, pectinate, toothed or entire lamina in the distal zone beyond the ovule-bearing stipe.
Seeds: subglobular to ellipsoidal, with a yellow, orange or brown fleshy
outer sarcotesta, and with or without spongy tissue beneath the inner
woody sclerotesta. 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 platyspermic;
germination cryptocotylar.
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