Anatomical and cytological studies of an intergeneric hybrid, Oryzopsis hendersonii × Stipa lemmonii (Gramineae)

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Abstract
A hybrid between Oryzopsis hendersonii and Stipa lemmonii is reported and formally described. In a population in central Washington where the two parent species are sympatric 12 hybrid plants were found. The hybrids are morphologically and anatomically intermediate; O. hendersonii, which occupies drier sites, has xeromorphic modifications in the leaves not found in S. lemmonii. Both parents and the hybrid have 2n = 34 chromosomes. Meiosis in the hybrid is abnormal with some unpaired chromosomes, clumping of the chromosomes at diakinesis, and lagging univalents at later stages. Univalents tend to divide synchronously at anaphase I, following the division of bivalents. An average of about 11 bivalents is determined. These studies may be interpreted as supporting the transfer of this Oryzopsis to Stipa which is presented here, and it is suggested that several species of Oryzopsis have evolved independently from stipoid stock.

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