Phacelia argillacea

Clay phacelia is very closely related to PHACELIA GLANDULOSA Nutt., a west slope Idaho, Wyoming, and Montana native. In fact, the original collection of clay phacelia in 1883 by Marcus E. Jones, in the vicinity of Pleasant Valley Junction, Utah, was identified P. GLANDULOSA. In 1894, Jones again collected the species; this time at Clear Creek near Soldier Summit in Utah County, Utah. When N.D. Atwood rediscovered the Clear Creek population in 1971, he found it to differ substantially from P. GLANDULOSA. He subsequently described and named it P. ARGILLACEA in 1973 (Gill et al. 1982).

Two plants which grow in association with Clay phacelia, the frequent adventive, CYNOGLOSSUM OFFICINALE (Hound's tongue), and the less frequent native, MENTZELIA LAEVICAULIS, are most readily confused with P. ARGILLACEA. Like Clay phacelia, they both produce basal rosettes. Hound's tongue's leaves, however, are entire and pubescent. MENTZELIA can also be distinguished by its leaves which are lobed with retorse or "velcro-like" hairs (England 1989).

BIOLOGICAL HABITAT: Clay phacelia occurs on steep slopes in sparse juniper-pinyon and mountain brush communities (Welsh 1987). The dominant species at the site of the largest element occurrence are RHUS TRILOBATA and AMELANCHIER ALNIFOLIA. At the base of the main slope is a degraded sagebrush steppe. Large and probably influential ungulates are deer, elk, and domestic sheep. Probably the most significant component is mule deer (England 1989). There is mainly wintertime use by big game, and (before a fence was built) transient but heavy spring and fall use by domestic sheep.

Specific plants which grow in the community surrounding the largest Clay phacelia occurrence are: STIPA HYMENOIDES, ELYMUS SIMPLEX, ERIOGONUM BREVICAULE, MENTZELIA LAEVICAULIS, MAHONIA REPENS, OENOTHERA CAESPITOSA, MARRUBIUM VULGARE, CYNOGLOSSUM OFFICINALE, AMELANCHIER ALNIFOLIA, RHUS TRILOBATA, ATRIPLEX CANESCENS, ARTEMESIA TRIDENTATA, CHRYSOTHAMNUS NAUSEOSUS, CERCOCARPUS MONTANUS, ROSA WOODSII, PINUS EDULIS, and JUNIPERUS OSTEOSPERMA. Less frequent plants which also occur in the community are: BROMUS TECTORUM, IVA AXILLARIS, CHENOPODIUM FREMONTII, SYMPHORICARPOS OREOPHILUS, QUERCUS GAMBELLII, CARDUUS NUTANS, AND JUNIPERUS SCOPULORUM (Gill et al. 1982, England 1989, Harper 1990).

PHYSICAL HABITAT: Climate: No long-term weather data exist for the area of the extant populations of this element. Climatological data from a nearby mountain area would represent that of a significantly higher elevation. Similarly, data from a different nearby station would reflect that of a lower valley elevation. The general climate for all of the element occurrence sites can, however, be classified as cool and subhumid (England 1989). A university study (see below) has had instruments nearby.

EXPOSURE: The majority of plants grow on slopes facing west through southeast. The exposure at one site is south and southeast (Gill et al. 1982, Armstrong 1990). The aspect at the other site is also southeast (England 1989). Both sites are free of snow, at least once during the winter, and are typically dry in early spring (Gill et al. 1982). Finally, one subpopulation faces south, and the western subpopulation's aspect is west (Franklin and Tuhy 1989).

SLOPE: At each site, the plants occur on a xeric, exposed slope of the Green River Formation, somewhere between 6000 and 7000 feet elevation (Franklin and Tuhy 1989). The slope at the site which holds the largest number of plants was measured at 70 percent (Armstrong 1990). One occurrence is easily and frequently disturbed by both biotic and abiotic influences. As a result the loose shale on the surface almost continually sloughs down the face of the platey slopes.

SUBSTRATE: The phase of the Green River Formation differs between sites. In each case it is described as a "shaley clay colluvium" (Gill et al. 1982). One occurrence is on a "fine-textured clay derived from a poorly consolidated shale member of the formation" (Gill et al. 1982). The platey shale at one site appears reddish-brown. However, Gill et al. (1982) indicate that the roots of the plants at this site penetrate a buff-to-gray-colored substrate.

One population occurs principally on "a narrow band of fine-textured reddish-brown clay from weathered faces of the Green River Formation" (Franklin and Tuhy 1989). However, further exploration resulted in the location of additional plants growing in a "grey-white, small fragmented shale occurring above the reddish-brown clay layer" (Franklin and Tuhy 1989).

Analysis of a soil sample from one site revealed a pH greater than eight. Further, greenhouse cultivation of the seedlings in native and artificial soils indicates that the clay composition of the native soil enhances its ability to hold moisture, even under conditions of high solar radiation (Kobler 1989).

GERMINATION REQUIREMENTS: Little is known about the germination requirements for Clay phacelia, but steps are being taken to increase our knowledge. Embryo viability of seed collected in June 1988 was tested by means of a tetrazolium (TZ) test. The TZ equaled 95% or 19 viable seeds out of the 20 tested (Matheson 1989). Additional seeds have been collected in June 1989 and on August 21, 1989, but they have not been cleaned or tested yet. Mary Alyce Kobler (Botany, University of Utah), conducted germination studies on PHACELIA LINEARIS and found that seed germination was cued by day length and temperature relationships. She initiated studies on seed germination requirements for P. ARGILLACEA in the fall of 1989 (Matheson 1989). To date seed germination EX SITU has been difficult.

ESTABLISHMENT: Dispersed seeds lodge in cracks or crevices on the shale-covered slopes and germinate when the right (unknown) set of conditions exist. Initial foliage leaves are small, but basal rosettes are formed by early to mid-October. They then over-winter, growing slowly underneath the snow pack. The plants begin to bolt, when the snow melts and the soil temperatures reach sufficient levels in the spring. This usually occurs in May. By late May, the first flowers begin to appear. The plants continually produce more flowers and increase in size, until late June or early July. Prolonged flowering seems to be related to moisture availability. In 1979, flowers were observed as late as mid-October (Gill et al. 1982).

Rosettes which have been dug and removed for EX SITU research and captive propagation in cooperation with the Center for Plant Conservation revealed unexpectedly shallow roots (Matheson 1989). These same plants, which are now in six-inch pots, are being grown in different soil mixes, including native soil, to gain insight into cultural requirements. To date, no significant observations can be reported; however, the rosettes in the vermiculite/perlite soil mix seem to be doing the best (Kobler 1989).

MAINTENANCE: No formal studies have been undertaken to determine basic maintenance requirements for Clay phacelia. However, it is England's (1990) observation that P. ARGILLACEA is dependent upon available, disturbed ground, with little or no competition. He speculates that if the Tucker site were somehow stabilized, P. ARGILLACEA would probably be extirpated. Harper (1990) further theorizes that, if site stabilization did occur, ELYMUS SIMPLEX would tend to dominate, which in the absence of grazing could force extirpation of the species from the Tucker site.

P. ARGILLACEA brings to mind the "chicken or egg" paradox. With the current limitation of knowledge regarding population variances, it is difficult to ascertain the importance of observed population variations in rosette-to-mature-plant ratios (England 1989).

DENSITY AND SUCCESSIONAL STATUS: Extant populations of Clay phacelia cover only three to five percent of the slope's surface area in the patches where they occur. Overall vegetative cover is about ten percent in these same areas of critical habitat (England 1989).

Due to recurrent natural disturbances which erode the surface of the four sites where the plants grow, P. ARGILLACEA can be categorized as a specialized micro-disturbance niche plant (Harper 1990). He notes that some 100 to 125 species have adapted this strategy along the Wasatch Front. The strategy Harper (1990) explains is one of opportunism. Micro-disturbance species are the first to germinate and establish themselves in new areas which have been exposed through some form of natural disturbance (e.g., hooves along the edge of a deer trail or wind and water erosion down a gravelly bank).

HEDYSARUM BOREALE, CLARKIA RHOMBOIDIA, and many PENSTEMONS are examples of plants which are specialized to survive under such conditions. Large disturbances, which are often caused by man's impact on a natural area, can create serious difficulties for some specialized micro-disturbance niche plants. In particular, native annuals frequently "fall apart" on large sites due to increased wind and solar radiation (Harper 1990).

REPRODUCTIVE STRATEGIES: Clay phacelia reproduces sexually. It is unknown whether this species is an obligate selfer, a facultative selfer, or an obligate out-crosser (Harper 1990). England (1989) surmises that apomixis is not part of this taxon's reproductive strategy.

The clay phacelia is considered a winter annual (Atwood 1975), but recent observations suggest that some of the plants in at least one of the extant populations might be simulating the life cycle of a true biennial (England 1989). In addition, observations in the fall of 1988 and the following growing season of 1989 imply that some of the individuals have also simulated the life cycle of a summer annual (Franklin and Tuhy 1989).

Seeds typically germinate in spring and fall, although they sometimes germinate in mid-summer if there is enough available moisture (England 1989). The plant blooms in late July, but non-flowering rosettes have been observed in both June and August (Matheson 1989).

England (1990) speculates that some plants which germinate early in the growing season have insufficient food reserves to initiate flowering the same year. These juvenile or vegetative plants must then over-winter before floral initiation and seed production are possible the following spring. England (1989) verifies that advanced plants have been observed in the spring with early flowering in late May or early June.

Since qualitative monitoring began in the early 1980s, the majority of the Tucker plants have reproduced as winter annuals (England 1989). In this case, the seeds germinate in the fall. Enough biomass is then generated in the fall and subsequent spring, provided they survive the winter, to initiate flowering in late June.

POLLINATION: The pollen vector is unknown; however, a 1988 Bee Biology and Systematics Lab field collection at the Tucker site "yielded the largest series of specimens recorded of a rare species of colletid bee, HYLAEUS GRANULATUS" (Tepedino 1989). Although the very first observed females of this rare bee were among the specimens collected, Harper (1990) surmises that this bee species is far too rare to be the primary pollinator for Clay phacelia. He further speculates that wind, or the more common ground-nesting bees in the area, could prove to be the major pollinators for Clay phacelia. Wind-pollinated species, he adds, tend to have greater genetic diversity.

SEED BIOLOGY/ECOLOGY: As indicated in the technical description, Clay phacelia has the capacity of developing four mature seeds per fruit. In the summer of 1987, England (1989) estimated that as many as 8000 seeds were produced on one adult winter annual. The plant held 200 cymes, with ten flowers per cyme and four seeds per fruit. Needless to say, Clay phacelia can be a very prolific seeder. The seed is produced sequentially over time. Cymes last for about ten days to two weeks. Flowers open daily along the cymes and persist for days before developing into fruit (England 1989).

GENETIC LOAD: Harper (1990) emphasizes the need to gain an understanding of the genetic load ("those genes which are lethal or sublethal in a homozygous state") that this rare plant is carrying. He indicates that studies are necessary to determine the ovule-to-seed ratio within the various populations. This should provide clues to whether the plant is an obligate selfer, facultative selfer or an obligate out-crosser. Obligate selfers, he says, have approximately 90% flower-to-fruit conversion rates, and out-crossed plants have approximately 50% flower-to-fruit conversion rates. By knowing the average number of ovules per flower and the average number of viable seeds produced per number of ovules, one can calculate the approximate number of lethal alleles per ovule, or "conversely determine the efficiency of the pollen vectors" (Harper 1990).

DISPERSAL MECHANISMS: No formal studies have been conducted on dispersal mechanisms. It is surmised by England (1989) that short distant seed dispersal is achieved primarily by wind, water, and gravity. Rosettes are generally located below or in association with mature adult plants. Some long-distance dispersal may be achieved through grazing and defecation, but the plants are probably grazed prior to seed set (England 1989).