Abstract

The systematics of the genus Astrebla were studied with use of morphological, distributional, anatomical, and breeding characteristics. Results show that the genus is a group of closely related but well-defined species. The occurrence of F₁ interspecific hybrids is strongly suggested from field observations and glasshouse plantings but because of sterility in the F₁ generation hybridization between species apparently plays little part in continuing evolution.

Species distributions are closely correlated with the occurrence of cracking clay soils and show large discontinuities. Although Astrebla pectinata, A. elymoides, and A. Squarrosa are common on the Barkly Tableland A. lappacea is generally absent from that area.

. Internal and epidermal leaf anatomy indicates that Astrebla is related to the chloridoid line of grasses.

Prevention of cross-pollination showed that all species are highly self-compatible. Circumstantial evidence suggests that large-scale apomixis does not occur.