Shrubs Of The Great Basin: A Natural History

Purple Sage

Purple Sage Salvia dorrii I ONCE ASSUMED that Riders of the Purple Sage, by Zane Grey, referred to our desert or purple sage. To my chagrin, I later learned that this famous western author was simply guilty ofa little artistic license in calling our com, mon sagebrush, an entirely unrelated plant, purple sage. Purple sage is a true sage, since it belongs to the same genus as the cultivated Salvia used in the culinary arts. Like the latter, the purple sage has the strong, aromatic, char, acteristic sage fragrance. In one species of California sage, it has been found that the volatile terpenes produced by the leaves appear to interfere with the germination and growth of grasses. This kind of competitive chemical be' havior by plants is known as allelopathy. The purple sage in the Great Basin characteristically grows on dry slopes and rocky bluffs in sagebrush associations. Except when in bloom, it is sel, dom abundant enough to attract much attention. Ordinarily it appears as a low, rounded shrub, seldom taller than 60 centimeters. The gray, finely pubescent, and rounded leaves-I to 2 centimeters long-persist to some extent through the winter. The blue flowers are borne in erect, interrupted spikes, with conspicuous bracts colored pink to purple surrounding them. Like the other members of the mint family, to which it belongs, purple sage has two,lipped flowers. Botanists recognize two basic types of flowers with regard to the symmetry of petals and sepals. If a flower has an arrangement like that of the lily, in which all the sepals and petals are alike, and the fl~wer is essentially circular in outline, it is referred to as being regular or actinomorphic. Such symmetry is regarded as radial. On the other hand, ifa flower has the kind ofsymmetry exemplified by an orchid, it is regarded as irregular or zygomorphic. In such Purple Sage 240 LAMIACEAE flowers there is only one plane of symmetry-there is only one way to split the flower, with one half looking like the mirror image of the other half. Irregular flowers are somewhat better adapted for specialized insect visi~ tors, and many forms can be effectively pollinated by only one kind of in~ sect. Many have evolved ways to insure that any visiting pollinator will suc~ cessfully transfer pollen from the stamens of one flower to the receptive stigma on the pistil of another flower. This complex arrangement ultimately makes for a more efficient system in terms of the number of seeds produced compared to the number of pollen grains formed. One could say that it was very energy~efficient, at least for the plant involved, although the insect ob~ viously expends a lot of effort by flying to various flowers in order to collect pollen and nectar. This increased efficiency does not necessarily mean that such irregular flower types will eventually take over the plant world. One has only to consider the very successful grasses, all of which are wind~ pollinated. In sage flowers, the upper lip is composed of two fused petals, while the lower comprises three fused petals. There are four stamens, but only two of these are fertile. The supporting stalk for each stamen is fused at the base with the corolla, a collective term for the petals. In the young flower, the two fertile stamens are arched over in such a way that a bee attempting to get at the nectar at the base of the flower will force the anthers of the stamens to dust its back with pollen. At this stage, the receptive stigma is held high, out of the bee's way, under the arch formed by the upper lip of the flower. After the pollen has been shed, the stalk supporting the stigma elongates and arches over into a position which allows it to contact the back of any bee entering the flower. In this way, self~pollination is avoided and cross~pollination is assured. The offspring resulting from the latter are more variable and thus confer an evolutionary advantage on their species. Like irregularity, fusion of the stamens and petals is considered an ad~ vanced evolutionary feature. Although not significant as such in the Great Basin, the various species of Salvia are important bee plants in California and thus important in the production of honey. In common with that of other members of the family, the species' pistil is a fouf...