On the taxonomic position of Eucommia ulmoides Oliv. (Eucommiaceae)

Summarizing, it appears that Eucommia has the greatest number of characters in common with the Urticales. This is shown by the similarity of the inflorescences as well as by the unisexual flowers and the dioecy. In both groups the pistil consists of 2 connate carpels and the ovary is usually 1-celled by abortion, while the stigmata are generally papillate. Further general points of relation with the Urticales are the originally spiral phyllotaxis, which becomes later on pseudo-distichous, simple vessel perforations, libriform with bordered pits, unicellular hairs and the occurrence of calciumcarbonate and silica as well as of latex elements. Yet, it seems difficult to indicate any particular family in the Urticales to which Eucommia should be most related. While the fruit recalls Ulmus and the latex elements Urtica and Cannabis, the spirally thickened vessel walls remind us of some Morus species. In addition, Eucommia is isolated by the facts that in the Urticales the perianth is never entirely wanting, that there is only one ovule in the cell of the ovary, that stipules are very frequent, that calciumoxalate is characteristic (it is wanting in Eucommia) and that the superficial suberization is subepidermal in the Urticales and epidermal in Eucommia. After the Urticales the Euphorbiaceae-Hippomaneae seem to be the nearest of kin, on account of a number of anatomical and morphological characters. However, the Euphorbiaceae usually possess a 3-celled ovary, a 2-celled one occasionally occurs in the Hippomaneae. Next follow the Hamamelidaceae which have, however, two fertile carpels but of which Distylium and Altingia show a reduction in the perianth and the latter moreover a similar leaf shape.