| BEN |
| BOTANICAL ELECTRONIC NEWS |
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| ISSN 1188-603X |
| No. 313 September 5, 2003 | aceska@victoria.tc.ca | Victoria, B.C. |
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Lasthenia glaberrima DC. is a member of the Asteraceae (tribe Heliantheae) previously known from southwest Washington State (Horsethief Lake State Park, Klickitat County [Florence Caplow, pers.comm.]) south to the central coast of California. There is also at least one documented observation in San Diego County (NatureServe 2003, CalFlora 2003).
Lasthenia glaberrima is a distinctive annual member of the Asteraceae. Its leaves are opposite, entire and linear. Each head is subtended by an unusual involucre composed of 5-10 phyllaries fused for most of their length to form a bell. The ray flowers have short, inconspicuous ligules hence the plant appears rayless. The achenes bear a pappus of fewer than 10 narrowly tapered to elliptic scales (Ornduff 1993).
It had not been found in Canada prior to May 25, 2003 when Gerry Ansell found it at East Sooke Regional Park, 20 km southwest of Victoria, British Columbia. I subsequently visited the site and described the habitat and population as follows.
The plants occurred in a muddy depression on the crest (approximately 6 m asl) of a coastal bluff. The 2 x 20 m depression was wet at the time but dries out by mid-summer. Other species included Alopecurus geniculatus, Plantago elongata, Poa annua, Hypochaeris radicata and Anthoxanthum odoratum. There were several deer hoof-prints in the depression, which may serves as a valuable water source in the late spring. A hiking trail passes by the population but there was no evidence of human trampling in the depression.
The population consisted of approximately 120 flowering individuals ranging from 8-20 cm tall. The plants were vigorous and flowering profusely. Immature achenes were already evident and it appeared the plants would survive long enough to produce viable seed before the depression dried up. The plants did not suffer significantly from competition with other species, nor is there evidence of substantial grazing or trampling by deer.
The disjunct occurrence of Lasthenia glaberrima on southeast Vancouver Island parallels that of many other species with similar distributions. The sub-Mediterranean climate of Victoria and the Georgia Basin is anomalous along the Pacific Northwest coast and may account for the disjunct occurrences of Allium amplectens, Crassula connata, Clarkia purpurea ssp. quadrivulnera, Dryopteris arguta, Isoetes nuttallii, Juncus kelloggii, Minuartia pusilla, Lupinus densiflorus, Montia howellii, Ranunculus californicus, Trifolium depauperatum, Triphysaria versicolor and Woodwardia fimbriata).
References
The genus Lasthenia (Asteraceae: Heliantheae) provides numerous opportunities to examine the link between adaptation to substrate and reproductive isolation (Rajakurana 2003). Commonly known as goldfields, plants of Lasthenia occupy large areas of the Californian landscape, casting spectacular carpets of brightly-coloured golden yellow flowers in early spring. A recent molecular phylogenetic study recognized 21 species and subspecies belonging to seven sections (Chan et al. 2001). All but one species are endemic to California and the Pacific Northwest. Lasthenia kunthii (Less.) Hook. & Arn., the only member of the genus found outside western North America, is endemic to vernal pools in central Chile (Ornduff 1966). Since many endemic species of vascular plants are edaphic endemics (Kruckeberg 1969, 1986), studies of a model genus such as Lasthenia could provide general insights into speciation in a variety of other edaphically diverse genera.
The Common Goldfields, Lasthenia californica sensu Ornduff (Ornduff 1993), is a winter annual growing in a variety of habitats in the Californian Floristic Province. Recent molecular studies suggest that L. californica sensu Ornduff consists of two species, L. californica subsp. californica and L. gracilis (Chan et al., 2002). These two species consist of two races differing in flavonoid pigments (Desrochers & Bohm 1993, 1995) and edaphic tolerances (Rajakaruna & Bohm 1999). Race A plants contain sulfated flavonoids and are found in ionically-stressed habitats such as serpentine outcrops and alkaline flats. Race C plants lack sulfated compounds and are restricted to dry yet ionically-benign habitats. The races are physiologically differentiated to deal with key ecological features that are associated with their distinct edaphic habitats. Race A is better adapted to deal with ionic stresses, specifically with sodium and magnesium, ions that characterize their edaphic habitat (Rajakaruna et al. 2003a). Measures of ion uptake, germination, survivorship, and root length suggest that tolerance to ionic stresses by race A plants is not based upon ion exclusion, pointing to internal mechanisms of tolerance. In contrast, race C is better adapted to drought, a feature that characterizes their edaphic habitat (Rajakaruna et al. 2003b). Race C is better able to avoid drought by faster growth to reproductive maturity and tolerate drought via allocating relatively more biomass to reproduction. Since both races achieve greater fitness under conditions that best match their natural environment, it is likely that the unique distribution pattern of the races has been achieved through differential adaptation.
The edaphic races are also reproductively isolated via various means (Rajakaruna & Whitton, unpublished) and it is likely that isolation has been enhanced as a bi-product of ecological selection. The parapatric races at Jasper Ridge Biological Preserve (Stanford University) show one of the lowest seed set, also suggesting the possibility of reinforcement of reproductive isolation at this site. The system now provides an ideal opportunity to seek associations between traits for adaptation (i.e., sodium, magnesium, and drought tolerance) and reproductive isolation (i.e., flowering time differences, pollen grain abortion and reduced growth, reduced hybrid viability).
A population genetic study conducted using RAPD markers (Rajakaruna & Whitton, unpublished) agrees with previous studies (Desrochers & Bohm 1995, Chan et al. 2002, Desrochers & Dodge 2003), supporting the notion of parallel occurrence of edaphic races in both L. californica subsp. californica and L. gracilis (Rajakaruna et al. 2003c). It appears that race A is ancestral to race C and that tolerance to ionic stresses is an ancestral trait in this complex. Sulfated flavonoids and traits associated with tolerance to ionic stresses appear to have been lost in race C populations of both species found under ionically-benign habitats.
The role of parallel evolution in the origin of species is at an early stage of discovery although there are several studies suggesting that traits or suites of traits may evolve independently in response to natural selection imposed by similar ecological forces (Levin 2001). The Lasthenia californica complex provides an ideal model to further both the hypotheses of adaptive differentiation and parallel speciation and conduct much-needed studies on the genetics of plant speciation.
References
Weighing in at 442 pages, this book is a thorough description of 89 aquatic weeds, with additional descriptions of 96 other species that might be confused with the most common weeds in western wet areas. While many of the weeds described are nonnative invaders listed as noxious on federal or state lists, the book also includes many native plants that may pose a nuisance to riparian users. Aquatic and Riparian Weeds of the West is inclusive of most of the submersed and floating-leaved weeds, but of necessity is more selective in treating emergent plants, including woody species.
For each of the 89 plant descriptions, the authors have prepared entries that include the common (based on the Composite List of Weeds by the Weed Science Society of America) and scientific names, Bayer code, noxious weed lists, synonyms, general information, descriptions life stages including seedling, mature plant, roots and underground structures, flowers, fruit and seed, habitat, ecological characteristics, distribution, propagation and phenology, cultural or mechanical methods that encourage or discourage survival, and a description of similar species (which often includes photos).
The photos by Jack Kelly Clark are nothing short of stunning. The thorough photocataloging of life stages (including seed and seedlings) is alone worth the cost of this book. The author's brief summaries for each species are also useful, and comparisons to similar species are very worthwhile.
While the inclusion of keys for separation of species may be a nice practice when you have a selected pool of plants, it is inherently misleading in that plants not included in this treatment may be misidentified. Likewise, the common names included in the Composite List of Weeds published by WSSA, and used as the authority for this book, are not necessarily the common names used by those "in the business," so it is best to know the scientific name. Synonyms are not generally included in the index. Species entries do not include references to other publications, although some genera have a short bibliography in the back of the book.
Potential readers should also bear in mind that this book is focused on the western US; some of the troublesome weeds of the eastern US are not mentioned. While some cultural management techniques are mentioned, the authors purposely avoid making specific recommendations on how to control the weed species described. This book will not tell you the best techniques to manage aquatic and wetland weeds of the west; biological and chemical control techniques receive no mention whatsoever. Personally, I think this book is an outstanding example of the genre, so long as readers bear in mind the limitations.
The target audience of this book is not the casual user of Peterson guides, but rather the professional resource manager seeking to identify and understand their weed species. It would also be helpful as an identification tool on selected species for resource managers, scientists, and professionals with interests in wetlands or riparian areas. At 442 pages, this is not a pocket identification guide, though it would fit in a large fanny pack or daypack. I would recommend this to aquatic and wetland professionals in the western US, and possibly the rest of the United States so long as readers bear in mind that it focuses on western aquatic weeds.