Division Cycadophyta > Order Cycadales > Family Zamiaceae > Subfamily Encephalartoideae.
Dioons are palm-like plants native to Mexico and Central America.
Most are under 1 -2 m high.
The cylindrical stem/trunk can be above or below ground and usually carries many leaves.
The leaf stalks are thickened at the base.
The once divided leaves are spirally aranged and interspersed with scale-leaves.
Leaflets are simple, often with spines and the lower leaflets are often reduced to spines.
Leaflets have no midrib and have forked, parallel veins.
Male and female plants both have stalked cones with spirally arranged sporophylls.
The male microsporophylls have flattened tips which bend up and there are no microsporangia under the tips.
The female megasporophylls have wide, flattened, overlapping tips that bend upwards and they usually have 2 ovules each.
Seeds, up to 4 cm, have a white or cream outer coat.
Dioon is divided into 2 groups.
1. The “Edule clade”, with leaflets under 15 mm wide, contains most species.
2. The “Spinulosum clade”, with 3 species, have wider, straight leaflets –
- D. rzedowskii (no spines on the petiole);
- D. mejiae (spines on the petiole, leaflet edge entire) and
- D. spinulosum (spines on the petiole, leaflet edges with spines).