Note on Haplopappus gracilis and H. ravenii-a Reply

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Abstract
In the preceding number of this journal, Arthur Cronquist suggested that Haplopappus gracilis and H. ravenii are not distinct species, and that the latter is a cytological race of the former. Published articles (Jackson, 1962; Jackson & Crovello, 1971) have carefully pointed out that these taxa are distinguishable on the basis of one or more morphological characters, as well as those of a cytological nature. One result of the paper by Jackson & Crovello (1971) was to show that numerical alignment of the races of the two species was inaccurate when up to 31 characters were used. However, when one constant morphological character of H. ravenii was utilized, 100 percent accuracy could be obtained. In addition to morphological distinctness, F1 hybrids between the two species are highly (80-96%) pollen sterile. The species have adjacent distributions in some areas, but no evidence of natural hybridization has been found. Cronquist cited one of my papers (Jackson, 19'64) in which he states that I declined either to describe as a new taxon, or to refer definitely to either species, a race with n = 3. Perusal of the title of that article will answer this point for the reader. The n = 3 race of H. gracilis was referred to as "tribivalens" without implying any taxonomic status because I did not consider it worthy of any subspecific or varietal rank. The main purpose of the article was to present evidence for preferential disjunction of chromosomes. A later paper (Jackson, 1965) clearly delineated the n = 2 and n = 3 types as two chromosomal races of H. gracilis, and showed that gene exchange between the two is uninhibited for all practical purposes. Further unpublished data indicate that the n = 3 race was derived from the n -- 2. What we have then is a situation with two morphologically closely related taxa: H. ravenii (n = 4) and H. gracilis (n = 2, n = 3). Hybrids between H. ravenii and either of the chromosomal races of H. gracilis are highly sterile. H. ravenii can always be distinguished from the races of H. gracilis by at least one constant morphological character. Cytological characters can be used, but are unnecessary. In my estimation, the two taxa are distinct species as indicated by the distributional patterns, barrier to gene flow, and morphological distinctness. Those who disagree with this interpretation should be more explicit as to why they believe some other treatment is desirable or necessary.

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