Chromosome numbers and pollen types in the Epacridaceae

Abstract

Chromosome numbers are reported for 22 genera and 116 species of the Epacridaceae.

In the tribe Styphelieae, haploid numbers of 4, 6, 7, 8, 9, 10, 11, 12, and 14 occur. This numerical sequence does not represent a continuous siries either of decrease or increase, but is built up from polyploid and aneuploid changes on base numbers of x = 4 and x = 6. Polyploid series on base 4 are found in Cyathodes, Astroloma, and Leucopogon § Pleuranthus, on base 6 in Leucopogon § Perojoa, and on base 7 in Lissanthe. Aneuploidy is also found within genera, but is generally more characteristic of particular genera.

In the Epacrideae, the usual haploid numbers are 13 and 12, and only one case of polyploidy is reported. Two species of Sphenotoma possess haploid numbers of n = 6 and n = 7 respectively. The base number for the Epacrideae is probably x = 6, and a relationship between the Epacrideae and the Styphelieae at the 6-chromosome level may be accepted. Any relationship between the Epacrideae and the Ericoideae at an amphidiploid level is denied.

With the exception of probable autotriplolds in Lissanthe montana, meiosis is essentially regular throughout the family.

Tetrad-type pollen is characteristic of the Epacrideae. In the Styphelieae, the pollen is usually monad (S-type) and never truly single. Three variants in the pattern of pollen development occur in the tribe, modified monad (S-type), full tetrad (T-type), and segregating tetrad (A-type). Variants in pollen development pattern are associated with aneuploidy.

The Epacridaceae must have had an ancient origin. Features of species distribution suggest that many may be post-Miocene in origin. Most of the genera must have been established in the early Tertiary, and the differentiation of the two tribes, the origin of the monad pattern of pollen development, and some fundamental changes in chromosome structure in the Styphelieae, permitting a period of chromosomal instab~lity during their evolutionary diversification, must have been still more ancient.