Systematics and reproductive biology of Dodecatheon pulchellum s.l. (Primulaceae)
Date
1987
Authors
Suttill, Terri-Ann
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Abstract
Taxonomic relationships were investigated in Dodecatheon pulchellum s.l., a group of spring-blooming perennials centered in the Pacific Northwest of North America. A number of taxa have been recognized in the D. pulchellum group but their relationships and appropriate taxonomic treatments were unresolved.
The group shows considerable morphological variation and includes three ploidy levels with chromosome numbers 2n = 44, 2n = 88, and 2n = 132. In this study 48 chromosome counts are reported; ploidy levels have been estimated from pollen grain diameters for a further 313 specimens. A series of multivariate procedures, including principal components analysis and discriminant analysis, have been applied to morphological data obtained from specimens collected in British Columbia and adjacent areas. Environmental and genetic components of morphological and ecological characters for six populations were investigated in a common garden. Most morphological characters, including many used in taxonomic keys, showed phenotypic plasticity and there were strong genetic differences in ecological tolerance among the populations. On the basis of the morphological, cytological and ecological evidence this study has demonstrated patterns of variation corresponding to three taxa: Dodecatheon pulchellum (Raf.) Merrill var. pulchellum, Dodecatheon pulchellum var. watsonii (Tidestrom) C.L. Hitchcock, and Dodecatheon cusickii Greene. Dodecatheon pulchellum s.l. contains diploids, tetraploids and hexaploids. This species is glabrous to slightly pubescent. Dodecatheon pulchellum var. pulchellum is morphologically variable and is found in open, rocky areas that experience summer drought or in estuarine mudflats that are wet all year round. Dodecatheon pulchellum var. watsonii is found in subalpine habitats and is characterized by a short, delicate scape, small leaves and few flowers. Dodecatheon cusickii is a diploid species, consistently glandular-pubescent, and is found in dry habitats of southern British Columbia, Washington and Oregon between the Cascade and Coast mountain ranges.
Phenology and reproductive ecology of three Q. pulchellum populations (two of var. pulchellum and one of var. watsonii) on Vancouver Island were also studied. Development from visible buds to ripe capsules takes 15-17 weeks (March to July) for the low-elevation Q. pulchellum var. pulchellum populations and 9-10 weeks (July to September) for the Q. pulchellum var. watsonii population. Individual plants of Dodecatheon pulchellum have a short blooming period (1-3 weeks at low elevations) but because of low synchrony in blooming period among plants the total blooming season extends to 5-7 weeks. The plants of Q. pulchellum var. watsonii set considerably fewer seeds per capsule per plant than either of the other populations. Fruit set consistently exceeded 70% in the low-elevation populations but was more variable in the high-elevation population (88% and 27% in the two years examined). Reproductive losses in the low-elevation populations were from predation and in the high-elevation population from abortion of flowers. In one Q. pulchellum var. pulchellum population, aspects of the breeding system were studied in detail. Plants were found to be self-fertile but only if pollen was actively transferred to the stigma. Self-fertilized plants set significantly lower mean number of seeds per capsule per plant than outcrossed plants, indicating that barriers to selfing exist and that D. pulchellum var. pulchellum is predominantly outcrossed. Plants receiving additional pollen had similar seed set to naturally pollinated plants, indicating that seed set was not pollen limited. Best total seed germination for Q. pulchellum and D. cusickii was achieved with seven or eight weeks of cold, moist stratification. The proportion of seeds that germinated varied considerably between populations. Germination of seeds of D. cusickii was more rapid in response to stratification than those of Q. pulchellum. Dodecatheon pulchellum var. watsonii seeds required considerably longer periods of stratification for germination than D. pulchellum var. pulchellum seeds. The reproductive differences between Q. cusickii, Q. pulchellum var. pulchellum and Q. pulchellum var. watsonii supports recognition of these taxa.