A Biosystematic Study of the Phlox Cuspidata-Phlox Drummondii Complex

The emphasis in this investigation of the P. cuspi- data-P. drummondii complex was placed on field studies and experi- mental breeding. Chromosome counts were made from bud material collected from 50 populations representing all the taxa. All meiotic counts were n 7. Ecological information was gathered and generalized maps showing the distribution of each taxon considered were made. Populations of a hybrid and/or introgressed nature were noted. Three populations were analyzed using the scatter diagram technique of Anderson. One of these, a hybrid population, showed a recoin- bination spindle and supported the belief that the population was of hybrid derivation. Pure populations of the putative parental types were analyzed by the same technique. A total of 464 flowers were emasculated and pollinated; 21 of these crosses involved P. roemeriana as the pollen parent. Breeding cages were utilized in the study. P. drummondii var. littoralis showed a low degree of autogamy. P. cuspidata var. humilis was highly auto- gamous. The other taxa did not set any seeds by autogamy within the cages. The over-all average of normal-appearing seeds produced, as compared to the number theoretically possible, was 58 per cent. Although 771 seeds of normal appearance were obtained from the crosses within the P. cuspidata-P. drummondii complex, efforts to germinate these seeds proved fruitless. A brief systematic review is presented and a key to the annual taxa of Phlox is included. The authors recognize two species within the P. cuspidata-P. drummondii complex. Two varieties are recognized within the species P. cuspidata. Two subspecies are recognized in the species P. drummondii: Subspecies GLABRIFLORA which includes two varieties and subspecies DRUMMONDII with four varieties. Three new varietal combinations were made in this disposition: P. drummondii var. glabriflora (Brand) Erbe; P.d. var. goldsmithii (Whitehouse) Erbe; and P.d. var. tharpii (Whitehouse) Erbe.