Astragalus diaphanus is a rare plant endemic to the
John Day River drainage of north-central Oregon. This
species has several interesting features, including the
dimorphism of its fruit and its geographical isolation from
the two nearest taxonomically related species, which occur
in Colorado. This study addressed the species' distribution
and habitat, the taxonomic relationships between the
varieties of A. diaphanus, certain morphological comparisons
among the species, possible reasons for the rarity of A.
diaphanus, and the population biology of this taxon.
Astragalus diaphanus was found to be more widespread in
the John Day drainage than was previously known, but its
range has shrunk due to habitat loss along the Columbia
River. In this study, two varieties are recognized within a
single species, based on striking morphological differences
in pod forms which correspond to a break in geographical
distribution. Other morphological characters are similar
between the varieties. Flavonoid analysis and chromosome
counts support this taxonomic treatment. Further study is
needed to elucidate the relationships of A. diaphanus and
its taxonomic relatives in Colorado.
A low reproductive rate in A. diaphanus appears to be a
potential problem, possibly contributing to its rarity. The
species exhibits a combination of annual and biennial lifecycles.
Many annual individuals of A. diaphanus perish
without reproducing. This may be off-set by a large seedbank,
which is replenished sporadically by high production
in robust biennials.
There is not a need at the present time to provide
legal protection to var. diaphanus, the more widespread and
common taxon. However, var. diurnus has a very limited
distribution along the South Fork of the John Day River and
is represented by few populations. Many of these are
marginally viable, and there are active threats to the
existence of the latter variety. Astragalus diaphanus var.
diurnus should be afforded legal protection as an endangered
species. / Graduation date: 1991
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/38084 |
| Date | 07 December 1990 |
| Creators | Wright, Carolyn E. |
| Contributors | Chambers, Kenton L. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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