A biosystematic study of the the relationships of Hieracium gronovii L. H. venosum L. and H. traillii Greene (Compositae : Lactuceae)

The relationships of H. gronovii L., H. venosum L. and H. traillii Greene were investigated for two reasons. First, to determine if H. traillii represents a hybrid of H. gronovii and II. venosum and second, to determine methods of identifying natural hybrids between H. gronovii and H. venosum. Data from reproductive behavior, artificial hybridization, cytology, morphology and flavonoid chemistry were used.

Differences between species in reproductive behavior were noted. Although all three taxa are self-fertile, only in H. gronovii will self-pollination occur in isolated heads. In H. venosum and H. traillii, self-pollination does not occur in isolated heads.

Artificial hybrids between H. gronovii and H. venosum were easily produced. These hybrids appeared vigorous, and set viable seed when self-pollinated.

Cytological differences occur between the species. All three taxa are diploid, 2n = 9_II. Irregular chromosome pairing was not observed in any of the taxa or in artificial hybrids between H. gronovii and H. venosum. Meiotic abnormalities observed resulted from division failure and possible paracentric inversions (bridge and fragment figures). The highest frequency of meiotic abnormalities occurred in inter-populational hybrids of H. gronovii, suggesting that its tendency toward selfing has produced genetic differences between populations.

Multivariate analyses of morphology indicate that all three taxa are distinctive. Artificial hybrids between H. gronovii and H. venosum are also distinctive. Although hybrids exhibited a wide range of variability, they combined characters of the parents. They are best identified as possessing the wide ligules (at least 1-1/2 mm) of H. venosum and the hair types and distribution of H. gronovii.

All flavonoids isolated were based on the flavones apigenin and luteolin. A comparison of flavonoid complements suggests that all taxa have distinctive profiles. However, the presence of unidentified compounds, one each in H. gronovii and H. traillii, prevents a definite decision on this. Flavonoid data do not support the interpretation of H. traillii as a hybrid, as it lacks a distinctive compound found in H. gronovii.

The similarities of H. venosum and H. traillii in reproductive behavior, morphology and flavonoid chemistry indicate that these two taxa have a closer relationship to each other than to H. gronovii. Based on these data, the wide range of morphological variability in H. venosum and the small distribution and more specialized ecological preferences of H. traillii (when compared to H. venosum), it is hypothesized that H. traillii represents a schizoendemic species—the endemic result of gradual speciation—which evolved from H. venosum.