EMBRYOLOGICAL CHARACTERS AND THE TAXONOMY OF THE STIPEAE (GRAMINEAE)

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Abstract
Epiblast length and shape were examined in 39 species of the Stipeae, 29 of which are native to North America. In most species of Stipa examined the epiblast equalled or exceeded the coleoptile and was acute with or without a small V‐shaped notch at the apex. In contrast, in most species of Oryzopsis the epiblast extended no more than three‐quarters of the way up the coleoptile and was more or less truncate. Two other characters that tended to differ between Stipa and Oryzopsis were the overall shape of the embryo as seen in ventral view and the position of the tip of the coleorhiza. In Oryzopsis the embryo tended to be broader (length/width 1.0‐1.6) than in Stipa (length/width 1.5‐3.7) and the tip of the coleorhiza higher with respect to the base of the embryo.Some taxonomically significant variation was seen within each genus. The species of Stipa sect. Hesperostipa are distinguished by a deep, parallel‐sided apical notch. The placement of S. webberi and S. hendersonii in Stipa rather than Oryzopsis was supported by the characters considered here. The two species of Nassella examined were stipoid in their epiblast characters, but their over‐all shape and the position of the coleorhiza were oryzopsoid. The only species of Piptochaetium examined, P. pringlei, was typically stipoid in the characters examined.