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Volume 84, 1956-57
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Sterility and Future of A. × wallii

When observed on January 12, 1955, the hybrids were at anthesis, with anthers and stigmas exserted. It was not noted whether or not the anthers had dehisced. A fortnight later, January 25, some plants were still flowering, and on the majority the spikes had reached the ripened colour. On January 5, 1956, there were some plants at anthesis, but for the greater part flowering was over. Both A. enysii and A. scabrum had set seed, and the seed was at either the “milk” or the “dough” stage. On both visits in 1955 pollen samples were taken from several plants, stained, and mounted. Of the 969 grains examined none was filled, and all were classified as sterile. No seed was set on any of the hybrids examined. That this hybrid with 2n = 35 should be sterile is not unexpected.

It seems likely that A. × wallii will exist only in the F1; backcrossing to either parent is not held to be likely, and gene exchange in the present state of A. × wallii to be impossible. The hybrid could possibly double its chromosome number and arrive at a state of chromosome balance. Should amphiploidy occur, the then new

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species would resemble in many characters the F1. Although apomixis has been recorded in A. scabrum (Hair, 1956), it does not occur in A. scabrum Group Tawera. Any advantages that may have been derived from effective genes for apomixis are denied A. × wallii. At present A. × wallii seems of little evolutionary consequence in the flora of New Zealand.

The final proof that it is a hybrid would be its synthesis. Even without such experimental evidence there seems little doubt about its parentage and hybrid status for the following reasons:

  • i. A. enysii and A. scabrum are the only species of the genus found to date where the hybrids occur, despite purposeful searching in two successive seasons.

  • ii. The plants are for the greater part morphologically intermediate between A. enysii and A. scabrum.

  • iii. The plants totally failed to produce viable pollen in one season, and seed-set failed in two seasons.

  • iv. The chromosome number of A. enysii is 2n = 28 (tetraploid) and that for A. scabrum 2n = 42 (hexaploid); the hybrid is pentaploid, 2n = 35.

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