Dioon spinulosum  Dier ex Eichl. 1883

pronounced: dy-OH-awn spin-yoo-LOH-sum

(Zamiaceae – the coontie family)

common names:  Giant Dioon, Gum Palm

Dioon Dioon spinulosumGiant Dioon Dioon spinulosumfemale coneis derived from the Greek δις (dis), twice, and ωον (óon), an egg, referring to the paired seeds; spinulosum is from the Latin spinulosus, plenty of little thorns.

This is a cycad that comes from the limestone cliffs and rocky hillsides in the tropical rainforests of  Central America. It is one of the tallest of the cycads, and can grow up to 16 m high. It is found at fairly low elevations, up to about 300 m, and commonly grows out of cracks and pockets in the rocks. The seeds germinate in small fissures in the cliffs, and growth can be painfully slow until the roots find their way to a pocket of soil.

The trunk of a fully grown plant may be as much as 40 cm in diameter. It has shiny, stiff, light to bright green pinnate leaves up to about 2 m long, that radiate out from the trunk, in an upward nest shape. There are from about 120 to 240 leaflets on each leaf: these are small and flat, have tiny marginal thorns, and taper to a sharp point.

The Giant Dioon is dioecious – it takes two plants to produce viable seeds. The female cone is the largest of any gymnosperm; it can be anything up to 55 cm long, and weighs up to 13 kg, is covered with a dense wool, and contains up to 300 seeds. The seeds are creamy white, oval in shape, up to about 5 cm long by 3 cm wide. The plant photographed, with its female cone, was in a garden in Birt Street, Picnic Bay.

In cultivation, this is one of the most trouble-free cycads. It will withstand full sun, and can tolerate a little exposure to frost. It seems to grow more rapidly when exposed to some sun than in does entirely in the shade, and seedlings can become quite sizeable plants in the course of a few years, although it takes centuries to develop to its full size. It is, by a considerable margin, the most commonly grown Dioon.

It can also work as an indoor plant in a brightly lit spot, or in a conservatory. It can make an excellent feature plant in a tropical or desert landscape, often substituting for a true palm where a large crown is desired without the tallness of a palm’s trunk. It can also look quite spectacular in a small garden where space is at a premium, or as a striking understorey plant beneath a large tree, or under any structure that allows some sunlight to filter through.

Photographs takein in Picnic Bay 2014

Page last updated 14th November 2016







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