Mapping Species Distributions

PHYTOGEOGRAPHY OF THE NATIVE VASCULAR PLANTS OF BRITISH COLUMBIA

Arctic willow (Salix arctica), photo by Virginia Skilton. This is a circumpolar species.

by

George W. Douglas, Del Meidinger

and Jim Pojar

Text reprinted from the Illustrated Flora of British Columbia, Volume 8,
with permission.

The native vascular plant flora of British Columbia has a complex and varied history, especially with respect to glaciation.  It consists of a total of 2316 taxa within a number of floristic elements* and sub-elements.  These elements range from widespread cosmopolitan species to coastal endemics.  The synopsis presented here includes the major elements in the flora, some of their sub-elements, the number of native BC taxa within these and examples of representative taxa.

[*Editor's note: Species may be grouped with others that share similar distribution patterns to form what can be termed elements.]

Cosmopolitan Species

This is the widest ranging of our phytogeographic elements and contains those taxa that have a worldwide distribution in both hemispheres.  Only a small number of our taxa (27) belong to this element.  Some of these include Isolepis cernua, Hutchinsia procumbens, Juncus bufonius, Stuckenia pectinata, Triglochin maritima and Zostera marina.

Bipolar Disjuncts

Plants in this element occur in both the Northern and Southern Hemispheres.  This type of disjunction is not readily explained, although Raven (1963) has suggested that most of these plants probably reached their disjunct areas by long-distance dispersal relatively recently.  A total of 45 BC taxa belong to this element.  Typical examples include Lilaea scilloides, Osmorhiza berteroi, Pectocarya penicillata, Sanicula graveolens, Schoenoplectus americanus and Trifolium microdon.  

Circumpolar Species

This group of widely distributed plants contains 16% (365 in total) of our flora. Although this element could be further subdivided into circumboreal, circumarctic and circumalpine elements (sensu Schofield 1969), we have not attempted that here.  Representative species include Carex pauciflora, Hierochloe hirta ssp. arctica, Listera cordata, Potentilla nana, Salix arctica, Saxifraga hieracifolia var. hieracifolia and Senecio conestus (syn. Tephroseris palustris). 

Amphiberingian Species

This element includes species that occur on both sides of the Bering Sea, extending westward into Asia and eastward into North America.  The role of the Bering Land Bridge in the distribution of northern plants has been the subject of numerous floristic papers (e.g. Hulten 1937, Porsild 1955)  We have also included within this element a number of North Pacific Basin species that probably did not extend their ranges via the Bering Land Bridge, but rather by the Aleutian Island Chain.  Many of these North Pacific Basin species (i.e. Carex macrochaeta, Hymenophyllum wrightii and Platanthera chorisiana) are readily identified but many others, due to more continental distribution, are not. A total of 179 taxa (8% of the flora) belong to this amphiberingian element. Examples of these include Arnica lessingii, Antennaria monocephala, Cardamine oligosperma, Carex membranacea, Rumex arcticus, Senecio fuscatus (syn. Tephroseris lindstroemii) and Spiraea stevenii.

North American Maritime Species

Taxa belonging to this element occur along both the Pacific and Atlantic Coasts in North America and sometimes along the Arctic Coast. Some of the nine plants in this element include Salicornia virginica (syn. Salicornia depressa, Sarcocornia pacifica), Senecio pseudoarnica, Spergularia canadensis var. canadensis and Puccinellia pumila. 

North American Radiants

Plants in this element range across large parts of North America.  For this treatment,we have recognized this as a broad group, without sub-elements (i.e. American Boreal, southern North America, etc.). Twenty-six percent of the flora (a total of 612 taxa) occurs in this element. Representative species include Carex peckii, Platanthera orbiculata, Primula mistassinica, Senecio pauperculus, Solidago multiradiata, Sporobolus compositus and Vaccinium caespitosum. 

Cordilleran Species

This group contains species that occur primarily in the western Cordillera but which may have a small part of their range extending into more eastern or northern regions. These taxa comprise about 35% of the flora (a total of 816 taxa).  Typical examples of Cordilleran species are Arnica latifolia, Aster engelmannii (syn. Eucephalus engelmannii), Draba albertina, Lupinus wyethii, Phacelia sericea, Rubus pedatus, Saxifraga mertensiana and Senecio cymbalarioides.(syn. Packera streptanthifolia, Packera subnuda).

Alaska-Yukon-Northwestern British Columbia Endemics

This group consists of species restricted to Alaska, Yukon and immediately adjacent northwestern British Columbia and occasionally the Northwest Territories.  Most of these endemics probably originated in a large glacial refugium in northern Alaska and the Yukon. Some, however, must have persisted on unglaciated munataks or other areas farther south (Douglas et al. 1981).  A small number of these (25 taxa) have reached the mountains of extreme northwestern British Columbia. Representative taxa include Astragalus nutzotinensis, Douglasia gormanii, Montia bostockii, Oxytropis huddelsonii, O. scammaniana, Salix setchelliana and Senecio ogotorukensis. 

Pacific Coast Endemics

This element consists of mesophytic Pacific Coast species that have their ranges extending over large parts of the Pacific Coast between Alaska and Mexico.  The 238 taxa (10% of the flora) in this Pacific Coast element may be further subdivided into three sub-elements:

Entire Pacific Coast Endemics

These taxa have ranges that extend from Alaska to Oregon, California or Mexico. This sub-element consists of 56 taxa and includes species such as Cardamine angulata, Carex obnupta, Malus fusca, Oenanthe sarmentosa, Oxalis oregana, Poa laxiflora, Ribes bracteosum and Sedum oreganum.

North Pacific Coast Endemics

This sub-element includes 30 plants that have ranges between Vancouver Island and Alaska.  Ten of these plants have their main distribution in the Queen Charlotte Islands (Calder and Taylor 1968).  Representative species include Atriplex alaskensis, Castilleja unalaschcensis, Gentiana douglasiana, Lloydia serotina var. flava, Lupinus nootkatensis, Polystichum setigerum, Salix reticulata ssp. glabellicarpa and Senecio moresbiensis (syn. Packera subnuda var. moresbiensis).  

South Pacific Coast Endemics

The South Pacific Coast sub-element contains taxa with ranges that extend from Vancouver Island (usually the southern part of the Island) southward varying distances to Mexico.  In British Columbia, this sub-element consists of about seven percent of the flora (152 taxa) and is represented by taxa such as Artemisia suksdorfii, Aster chilensis (Symphyotrichum ascendens), Lomatium utriculatum, Sanicula arctopoides, S. bipinnatiida, Senecio macounii (Packera macounii) and Trifolium depauperatum var. depauperatum.  A few members of this sub-element (Bidens amplissima, Limnanthese macounii and Aster paucicapitatus) do not have ranges extending beyond British Columbia or northwestern Washington.

[Editor's note: Since the writing of this text, Bidens amplissima has since been reported from Washington and is likely present in Oregon.]

British Columbia Endemics

Another group of endemics of interest are the 46 taxa that occur in British Columbia and immediately adjacent regions (Douglas 1996).  Nine of these taxa are restricted solely to British Columbia and belong to two groups:  a Queen Charlotte Island/northern Vancouver Island/adjacent mainland group (7 taxa) and a southern Vancouver Island/adjacent islands and mainland group (2 taxa).  A total of 19 taxa are part of the Pacific Coast endemics described above, while the remaining 27 occur in the Cordilleran region of British Columbia and immediately adjacent states and provinces.

For references used in this article, please visit the General Referenes for the Illustrated Flora of British Columbia.