individual roots are thickened rhizomes and are inhabited by cyanobacteria of the genus Nostoc, which mainly used them for nitrogen fixation. There also seems to be a symbiotic relationship with arbuscular mycorrhizal fungi. Cones and Seeds All Dioons are dioecious, having either male or female organs, but only on different individuals. The male cone is stalked. The male cone scales called microsporophyll, which are flattened and bent upwards, sterile at the tip . They are arranged spirally around the pin axis. Each microsporophyll carries on its underside (abaxial side) a variety of pollen sacs. These open with slots, from which the pollen then escapes. The pollen grains are streamlined and have only one germ line (monosulcate). The male cones fall off after one year. The female cones are also stalked and can remain on the plant for more than a year. The female microsporophyll are more leaf-like than those of other cycads, the greatest similarity to those of the genus Cycas. The scales are flattened at the top, widened and bent up. Each sporophyll carries two, rarely three, ovules. These are straight to the axis (orthotropic), are inclined inwardly to this (inverse) and hang on the axis-facing side of the thickened scales. The opening at the tip of the ovules (micropyle) is very small, leaving only a narrow opening on the Nucellus. The megaspore sheath thickened from 3–4.5 microns in the young ovule to 9-10 microns in the mature seed. The number of archegonia varies between one and ten. The nucleus of the egg is unusually large. The largest female cones of the genus D. spinolosum shows up to 80 centimeters in length and a diameter of up to 30 centimeters. The seeds are spherical, ovate or ellipsoidal and reach a diameter between about one and four centimeters. They are surrounded by a fleshy, white or cream-colored seed coat. The seed coat consists of three layers, a fleshy outer and inner layer, between which a layer of stone cells lies. The embryo is straight with two cotyledons, these are fused at the top. The embryo carrier (suspensor) is very long and spirally twisted. The seeds are radiated (radiosperm). The germination takes place cryptocotylar, i.e. the cotyledons remain during germination in the seed. Distribution Dioon species can be found in Central America between the 15th and 29th northern latitude and are part of the Neotropical floral kingdom. The distribution area includes