Medullosales

The Medullosales is an extinct order of pteridospermous seed plants characterised by large ovules with circular cross-section and a vascularised nucellus, complex pollen-organs, stems and rachides with a dissected stele, and frond-like leaves. Their nearest still-living relatives are the cycads.

Most medullosales were small to medium-sized trees. The largest specimens were probably of genus Alethopteris, whose fronds could be 7 metres long and the trees were perhaps up to 10 metres tall. Especially in Moscovian times, many medullosales were rather smaller, with fronds only about 2 metres long, and apparently growing in dense, mutually supporting stands. During Kasimovian and Gzhelian times there were also non-arboreal forms with smaller fronds (e.g. Odontopteris) that were probably scrambling or possibly climbing plants.