A Cytological Study on the Genus Phlox

Abstract

(1) Chromosome numbers of 18 forms (35 varieties) of Phlox have been determined. The basic chromosome number is 7. Thirty-two varieties scattered among 15 forms contain 14 chromosomes in the body cells (or 7 in the germ cells). One of these forms (a derivative of a species cross) indicated a partial aneuploid condition-15 chromosomes being seen in some somatic cells. Of the other 3 forms examined 2 were tetraploid, with 28 somatic chromosomes, and the third one was apparently a triploid since it had 20+ somatic chromosomes. Gilia capitata, from a related genus, has 18 somatic chromosomes.
(2) Some morphological characters of the chromosomes are described.
(3) The known hybridizations among Phlox species are summarized.
(4) Three species hybrids were among the 18 forms worked with. Cytological irregularities in 2 of these (and especially in P. procumbens) are followed through the two meiotic divisions and are shown to result in abnormal microspore and pollen production.
(5) Mention is made of the types of sterility observed in several forms.
(6) A discussion is given which touches on some taxonomic and pbylocytological problems.