Dwarf woolly-heads, specific populations, COSEWIC assessment status report: chapter 3

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Species Information

Name and classification

Two varieties of Psilocarphus brevissimus have been described but var. multiflorus is restricted to central California. All other material belongs to var. brevissimus (Morefield 1993).

Morphological description

Psilocarphus brevissimus is a small, woolly, low annual herb arising from a short taproot (Figure 1). It has narrow, short, opposite stem leaves that are usually 5-20 mm long and 1.5-5 mm wide. The upper leaves usually surpass the flower heads.

The heads appear to be terminal on shoots but careful examination reveals they are born in the forks of inconspicuous branches. The heads lack involucres (rings of small bracts around the flowers which are present in most members of the aster family), rays or any showy structures and are copiously woolly and inconspicuous like the rest of the plant. Each head is lobed and the lobes appear to have derived from the incomplete combination of 4-5 heads into one. Each lobe contains a few central male flowers surrounded by anywhere between 8 and 80 female flowers. The female flowers are each partially enclosed by a minute, woolly, sack-like receptacular bract that has a lateral, translucent appendage. The bracts are about 3 mm long at maturity (2.5-4.0 mm). The style near the tip of the achene is offset (Cronquist 1950, Douglas 1998).

Although species in the genus Psilocarphus are relatively well defined (Morefield pers. comm.) “the character-combinations of the species interlock” (Cronquist 1950) and specimens are not always easily identified using a dichotomous key. Psilocarphus brevissimus can generally be distinguished from the other two members of the genus found in Canada - P. tenellus and P. elatior. Psilocarphus tenellus has shorter receptacular bracts (1.2 – 2.7 mm vs. 2.5 – 4.0 mm in brevissimus), its leaves tend to be widest at the tip (rather than at the base), and its achenes tend to be broadly oblanceolate to narrowly obovate (rather than oblanceolate) (Cronquist 1950). Nevertheless, P. tenellus and P. brevissimus may occasionally be hard to distinguish (Björk pers. comm. 2005). Psilocarphus elatior is more closely related to P. brevissimus. The receptacular bracts of both species are about 3 mm long. Psilocarphus elatior differs in being less densely woolly, has a simple rather than lobed receptacle, has a subapical rather than offset style, and tends to be more erect rather than prostrate. The achene of P. elatior tends to be turgid and narrowly oblong to elliptic-oblong, rather than flattened and oblanceolate as in P. brevissimus (Cronquist 1950). Specimens of P. elatior may occur found within the range of P. brevissimus var. brevissimus and look like the latter (Morefield 1993; pers. comm.).

Despite difficulties in identifying the species, Psilocarphus elatior, P. tenellus and P. brevissimus have been recognized as separate species for over a century, and were accepted as such in the most recent generic treatment (Cronquist 1950) as well as the soon-to-be-released treatment in the Flora of North America (Morefield pers. comm.).

Genetic description

Morefield (1993) reports that 2n=28 in Psilocarphus brevissimus and has indicated that this number is consistent among most members of its subtribe which have been examined (Morefield pers. comm. 2005). No other genetic information is available on the genetics of the species.

Designatable units

The Southern Mountain Population (Princeton area of British Columbia) and Prairie Population (Alberta and Saskatchewan) should be considered separate Designatable Units. There is a pronounced disjunction between the two units, which are separated by a distance of over 500 km and several north-south oriented mountain ranges including the Rocky Mountains, the Purcell Mountains, the Selkirk Mountains and the Okanagan Mountains. The Southern Mountain Population is probably derived from a source population farther south, but west of the Rockies. The Prairie Population is more likely to be derived from source populations east of the Rockies, in Montana or Wyoming. From a continental perspective, populations east of the Rockies appear to be only weakly linked with those from west of the Rockies. As a result, there has probably never been dispersal between the Southern Mountain Population and the Prairie Population in Canada, even indirectly through a Washington-Idaho-Montana corridor. Such dispersal is not likely to occur in the foreseeable future.

Furthermore, the two units occupy different eco-geographic regions as defined by COSEWIC: the Southern Mountain Ecological Area and the Prairie Ecological Area.

Morefield (pers. comm. 2005) characterized material collected from Alberta and Saskatchewan as taller and more elongate than is normal for the species.

Plants recognized in this report as belonging to the Prairie Population were previously identified and erroneously treated as the Prairie Population of tall woolly-heads (P. elatior) and designated as special concern by COSEWIC in May 2001. Specimens from Alberta and Saskatchewan were subsequently re-examined in 2005 by provincial vascular plant specialists from Alberta and Saskatchewan. These included: Dr. John G. Packer (Professor Emeritus, Botany, University of Alberta, Edmonton) and Ms. Joyce Gould (Alberta Natural Heritage Information Centre) and Dr. Vernon L. Harms (The Fraser Herbarium Dept. of Crop Science and Plant Ecology and Dept. of Biology University of Saskatchewan, Saskatoon). Their examination of specimens resulted in the re-identification of prairie specimens formerly considered to represent P. elatior as P. brevissimus. Dr. James D. Morefield, (Botanist, Nevada Natural Heritage Program) the world specialist on the genus Psilocarphus, has also examined Canadian prairie specimens and confirmed their identities as belonging to P. brevissimus. Specimens of P. elatior appear not to be found east of the Rockies, even in the United States (Hitchcock et al. 1955).