Rayless goldfields (Lasthenia glaberrima) COSEWIC assessment and status report 2000: chapter 3

Species Information

Name and classification

Scientific Name:
Lasthenia glaberrima A.DC.
Synonym:
L. minima Suksd.
English common names:
Rayless Goldfields, Smooth Goldfields
Family:
Asteraceae (aster family)
Major plant group:
Eudicot flowering plant

Lasthenia glaberrima is a clearly defined taxon that presents no classification problems. Dwarfed plants with small heads have been called L. minima Suksd. but that name has been rejected in modern floras because the differences appear to merely be a response to environmental differences (Ornduff 1966).

Morphological description

Lasthenia glaberrima is a fibrous-rooted annual with sprawling to erect, simple to freely branched and hairless shoots (Figure 1). The species may form adventitious roots from the lower stem nodes. Its leaves are oppositely arranged, 2-10 cm long, linear and lack hairs or teeth. The flowering structure consists of numerous flowering heads that are erect at anthesis but may bend down after flowering. Each bell-shaped head is 5-7 mm long and consists of an outer ring of 5-10 fused, hairy bracts. The individual flowers are tightly packed on a cone-shaped base within the fused bracts. The outer ring of 6-13 flowers have pale yellow, petal-like structures (ligules) which are so inconspicuous that they may easily overlooked. The inner (disc) flowers are more numerous, pale yellow and lack showy petal-like structures. The fruits (achenes) are less than 4 mm long, linear and hairy. Each fruit bears a cap (pappus) of up to 10 narrowly tapered to elliptic scales (Ornduff 1966, 1993).

Genetic description

Lasthenia has a base chromosome number of x=8. The genus is monophyletic and appears to have undergone an initial rapid radiation followed by long periods of adaptation and speciation. Evidence suggests that the substantial morphological, ecological, cytological and biochemical differences among species may be associated with the accumulation of rather few genetic differences (Ornduff 1976). Lasthenia glaberrima has a chromosome count of 2n=10 (Ornduff 1993). Ornduff (1966) felt that L. glaberrima was a rather advanced member of the genus but Desrochers and Dodge (2003) concluded that it was a primitive member of the genus based on Internal Transcribed Spacer (ITS) sequence data. The species is morphologically quite variable and is self-pollinated so there is a significant possibility of distinct genetic composition, particularly in isolated populations like the one in Canada (Chan pers. comm. 2005).

Figure 1. Illustration of Lasthenia glaberrima by John H. Rumley in Hitchock et al. 1955, with permission.

  1. illustration of Lasthenia glaberrima showing growth form
  2. flower head involucre of bracts
  3. a single flower with a short ligule from the outer ring of flowers in the head, and
  4. a single flower from the center of the flower head without a petal-like ligule
Figure 1. Illustration of Lasthenia glaberrima.

Designatable units

There is but a single occurrence and, therefore, a single designatable unit is recognized for this species in Canada.

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