When there is a single ovule, with its axis vertical, it may be attached to the placenta at the base of the ovary (basal placenta), and is then erect, as in Polygonaceae and Compositae; or it may be inserted a little above the base, on a parietal placenta, with its apex upwards, and then is ascending, as in Parietaria.
The more common plants in the most characteristic part of this region in southern Arabia are Capparidaceae, Euphorbiaceae, and a few Leguminosae, a Reseda and Dipterygium; palms, Polygonaceae, ferns, and other cryptogams, are rare.
The vegetation of the dry region of central Asia is remarkable for the great relative number of Chenopodiaceae, Salicornia and other Central salt plants being common; Polygonaceae also are abun Asia.
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