Trees or shrubs with secondary thickening and often with resin ducts. Xylem without vessels (except in Gnetopsida); tracheids are abundant. Leaves needle-like, scale-like or broad, sometimes 0. Flowers mostly unisexual; the staminate with pollen sacs (microsporangia), borne on the upper or lower side of stamens (micro-sporophylls); ovulate flowers consisting of ovules (macrosporangia), borne on a macrosporophyll or at -the end of a flower axis but not enclosed in an ovary (pistil absent). Pollen reaching the ovule directly (not via a stigma). Female prothallium many-celled, forming the endosperm and containing reduced archegonia. Seeds consist of seed-coat, a diploid embryo with 2 -to many cotyledons and a haploid endosperm.