Flora of North America species comparison

Primula Linnaeus sect. Dodecatheon (Linnaeus) Mast & Reveal

Species 17 (17 in the flora).

Members of Dodecatheon are widespread throughout much of North America, extending from northwestern Mexico to the Arctic in Alaska and northwestern Canada. Taxonomic boundaries between species are sometimes blurred, and the variation within the more widespread species (such as the eastern D. meadia and the western D. pulchellum) can be bewildering. Nearly all recognized species have an array of synonyms, and some names used in the past have proven to be illegitimate or misapplied, adding to the nomenclatural morass.

The genus can be subdivided into two groups (but not the three recognized by H. J. Thompson 1953), based primarily on the rugose (sect. Purpureo-tubulosa R. Knuth) versus smooth (sect. Dodecatheon) anther connective (A. R. Mast et al. 2004). Species with an enlarged stigma (notably Dodecatheon jeffreyi, the type of sect. Capitata H. J. Thompson) fall into the latter taxon. Even so, as noted in the key, both D. hendersonii and D. subalpinum occasionally have smooth connectives, and D. poeticum, a member of sect. Dodecatheon, has rugose connectives.

Recognition of Dodecatheon creates a paraphyletic Primula (M. Källersjö et al. 2000; A. R. Mast et al. 2001, 2004; L. Martins et al. 2003). Dodecatheon falls within Primula subg. Auriculastrum Schott (as sect. Dodecatheon) and is seemingly allied with the Sierra Nevada endemic P. suffrutescens A. Gray. The two share an involute leaf vernation. While Primula has a base number of x = 11, Dodecatheon has x = 22; H. J. Thompson (1953) has shown that 2n = 66 plants are triploids, not hexaploids. These observations have resulted in the transfer of all species of Dodecatheon to Primula (A. R. Mast and J. L. Reveal 2007). For those wishing to adopt this concept, the appropriate names are provided here in synonymy.

The morphological differentiation of the monophyletic Dodecatheon clade is the evolution of buzz-pollinated flowers (e.g., by bees, similar to that found in Solanum) coupled with a homostylous rather than the heterostylous floral condition typical of Primula (Mast et al. 2004). Coupled with this was fixation of recessive alleles at the heterostyly linkage group (pin phenotype) and at least six other traits that likely arose with the origin of Dodecatheon. One major change preceded its origin (flower coloration, a transfer exaptation in Dodecatheon), and another followed it (rugose anther connectives, an adaptation to buzz pollination). The first accounts for the shared floral colors among P. suffrutescens and Dodecatheon. The second, significantly, provides “footing” for the pollinator while buzzing the flower. In general, anthers with a rugose connective are larger than those with a smooth connective, and the anthers of Dodecatheon are considerably larger than those of Primula. Also related to these changes are the usually connate filaments forming a tube, thick connectives, and poricidal anthers (L. D. Harder and R. M. R. Barclay 1994).

Pollination studies in Dodecatheon are limited; only two species (D. amethystinum and D. meadia) have been examined in detail (L. W. Macior 1964, 1970b). According to H. J. Thompson (1953), flowers not visited by a pollinator can self-pollinate.

Use of the taxonomic rank of variety, rather than subspecies, was discussed by N. H. Holmgren (1994), and those concepts are followed herein.

Well-preserved flowers of Dodecatheon are critical for identification. The nature of the anther (especially whether the connective is smooth, longitudinally wrinkled, or transversely rugose) and the color patterns of the corolla are important observations that should be made in the field because the flowers often lose color when dried. Some species (D. hendersonii, D. poeticum, and D. subalpinum) are keyed twice, in part because the connective can easily be misinterpreted. In particular, one should check for bulblets (about the size of grains of rice) that are produced among the roots of some species at anthesis.

Vegetative plasticity in response to both moisture and time of season contributes to extremes in variation, especially height and robustness of plants, and length and breadth of leaves. Because some species of Dodecatheon tend to flower in moist soils of grassy meadows (or even in running water), but only in places that tend to dry out, the length of time a particular site is wet can be a significant factor in determining the overall size of the plant and leaves. Additionally, ecotypic variation has been documented (T. A. Suttill and G. A. Allen 1992). In some species, one can find an ecological gradient with some plants near a stream bank having longer, broader leaves than those on the drier slopes away from the stream. Because there is often a continuum, it is easy to notice in the field, if alert to variation within the population. In others that tend to be in moist places throughout most of their growing cycle, elevation is a factor that seemingly plays a role in the vegetative plasticity.

Adding to the complexity is the need to observe the valvate or operculate dehiscence of the capsule, and the degree of firmness of the capsule wall. Dehiscence of the capsule is clearly valvate in some species (e.g., Dodecatheon pulchellum) with no hint of a line of separation. In other species (e.g., D. jeffreyi), the capsule opens on a transverse line near the top of the fruit, shedding a cap (operculum) often with an intact style. There are specimens that have both valvate and operculate dehiscence even on the same plant (e.g., D. clevelandii). The distinction is further complicated by the “line of separation,” which is often distinguished by the distal portion of the capsule being a darker color and also, (in some) glandular. The operculum may consist of little more than the base of the style and may be well apical of the “line” that is indicative of the depth to which the capsule will split into five, ten, or more toothlike segments. With age, the (usually) inwardly curved teeth shed the operculum and then fall away resulting in what appears to be a toothless, circumscissile capsule. In contrast, valvate capsules develop teeth at the apex of the fruit, resulting (often) in a splitting of the style into parts. With age, the (usually) outwardly curved teeth shed the fragments of the style. The teeth usually remain attached to the body of valvate capsules; sometimes they are shed, resulting in what appears to be a toothless, circumscissile capsule.

Finally, be aware that occasionally two or more species may occur in proximity. Because the distinguishing features used here to recognize species can be difficult to observe without a critical examination of the flower, and in some cases the root system and capsules, a seemingly variable population may, in fact, be a mixture of plants of two different species with an occasional sterile hybrid added to the mix. This can result in herbarium collections composed of two species, adding even more difficulty to the identification of these plants.

Shootingstars are widely cultivated, and some cultivars have been selected. Essentially all species are found in nurseries. Most can be grown in sunny to lightly shaded places in dampish soil that slowly dries. Most flower during the spring months and are especially attractive when planted in masses. None of the species has much of a history of medicinal use by Native Americans. Flowers of some species were used decoratively, to attract men, and to aid youngsters to sleep. Roasted leaves and roots were eaten in California, and in the Pacific Northwest an infusion of roots was occasionally used as an eye wash, a treatment of cold sores, or an oral gargle (V. K. Chestnut 1902; J. Goodrich et al. 1980; J. C. Hellson 1974; E. V. Steedman 1930; N. J. Turner et al. 1980, 1990).

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Varieties 7 (7 in the flora).

The variation within Dodecatheon pulchellum is substantial and, for the most part, each of the entities recognized here seems distinct although nearly all break down in one or more features; most seem to have intergraded with other entities in the past. Variety pulchellum is the most widespread and remains, even as treated here, quite variable. The depauperate, often uniflorous, high-elevation form, var. watsonii, is included in var. pulchellum; there is no difference except in overall size even on the East Humboldt and Ruby mountains of northeastern Nevada, the type location of var. watsonii. Widely disjunct populations assigned to var. monanthum remain problematic. The plants of northwestern California and southwestern Oregon differ only slightly from those found elsewhere in Oregon, including the Blue Mountains, where the type of var. monanthum was obtained. The southern Utah expression, while similar morphologically, displays a biogeographic pattern that is unique. A better understanding of the variation between the western and eastern phases of var. monanthum is needed.

The coastal var. macrocarpum has consistent morphological differences and a higher ploidy level (2n = 88, 132) compared with the more inland var. pulchellum (2n = 44). Whether or not the ploidy level difference is consistent remains to be shown.

The arid forms of Dodecatheon pulchellum exhibit remarkable morphological differences that require recognition (J. L. Reveal 2005). Hanging garden plants in Utah are recognized as var. zionense, following N. H. Holmgren (2005). Some populations assigned to this variety may ultimately prove to be merely large-leaved plants of either var. pulchellum or the Utah phase of var. monanthum. Zion shootingstar may owe both its large leaves and its glandular-puberulent pedicels and calyces to hybridization with D. redolens sometime in its evolutionary past, even though the latter taxon is no longer close geographically. Variety shoshonense, usually growing in moist, alkaline meadows, is found mainly in the northern Mojave Desert and the Intermountain West. The color pattern associated with the stamens differs from most other varieties of the species, suggesting a fundamental change associated with pollination and likely a closer relationship to var. cusickii (which also has yellow pollen sacs) than to var. pulchellum.

This taxon inadvertently was named Dodecatheon puberulum (Nuttall) Nuttall three years before the establishment of Exinia pulchella. To avoid nomenclatural disruptions, the basionym D. meadia var. puberulum Nuttall has been proposed for rejection (J. L. Reveal and K. N. Gandhi 2008).

(Discussion copyrighted by Flora of North America; reprinted with permission.)