Evolutionary relationships of Phacelia linearis

One of the most widely distributed phacelias in North America is Phacelia linearis, a species) notably consistent in the morphology of its flowers and seeds. It is one of the earliest known phacelias, having been described from material collected by the Lewis and Clark Expedition. Asa Gray (1875) assigned P. binearis to the subgenus Elktoca, where he aligned it close to P. franklinii, an interpretation later concurred in by Brand (1913) and Howell (1945). It was necessary, therefore, to include P. tinearis in a recent experimental study (Gillett 1960) of the P. franklinii group and to test the relationships between this group and P. tinearis by several criteria, including genetic compatibility, growth pattern, floral morphology, and seed morphology. The object of this paper is to report the evidence derived from these studies and to present an interpretation of the evolutionary status of P. tinearis in light of this evidence. This species occurs from eastern Wyoming (map, Fig. 1) west to Puget Sound, and from central British Columbia south to northern California, over a range of elevations extending from sea level to approximately 2400 meters. It is usually found on dry washes and rock outcrops and is strongly associated with igneous formations, being relatively common on the lavas of the Columbia and Absaroka plateaus. It is an annual, and flowers as early as March and as late as July. Flower and seed morphology are seen in Fig. 2. The evidence reported here was obtained through the study of several hundred herbarium specimens and from extensive greenhouse cultures of Phacetia tinearis and of species of the P. franktlinii group. These cultures were established from seed or from living plants (denoted by asterisk) listed in Table 1. The extensive chromosome studies in the Hydrophyllaceae by Cave and Constance (1942, 1944, 1947, 1950, and 1959) have included three counts on Phacetia ltinearis, all n 11. This number has been confirmed by cytological examination of pollen mother cells from plants grown in the present study (Gitllett 1199). The consistent occurrence of 11 pairs of chromosomes casts little light on the evolutionary status of P. tinearis, for this same chromosome number characterizes all of the species in the P. franklinii group as well as nearly 70 additional species of Phacetia.. Plants of Phaceltia ltinearis are self-fertile, a feature that characterizes a large number of phacelias (Heekard 1960, Gillett 1955). Unattended plants of P. tinearis, however, rarely set seed, and selfed flowers will usually not set seed unless they are pollinated approximately two days after anthesis. In my own work 15 flowers pollinated at anthesis produced no fertile capsules, whereas 8 flowers pollinated two days after anthesis produced 7 fertile capsules. This indieates that protandry operates in P. linearis, undoubtedly to promote outcrossing. While out-crossing is advanced by flower structure in most species of the P. franktinii group as well as in P. tinearis, the evolution of protandry as a device to promote out-crossing is noted only in P. tinearis. The genetic isolation of Phacetia, tinearis from species of the P. franktinii group is clearly indicated by the negative results of controlled pollinations reported in Table 2.