7415 Empetrum L.
- L., Sp. Pl.: 1022 (1753).
Notes: Mirré, Elven, and Murray: Several early studies address the small genus Empetrum, including two early monographs (Good 1927; Vassiljev 1961), studies focusing on the variation in and distribution of diploids and tetraploids in Europe and the North Atlantic regions (e.g., Hagerup 1927; Blackburn 1938, 1939), and studies on the variation in morphology and ploidy levels in northeastern North America (e.g., Löve and Löve 1959; D. Löve 1960).
The most recent worldwide treatment is Vassiljev (1961) where he accepted 18 species in two sections and seven series. Vassiljev's system is based, foremost for the sectional division, on the colour of fruits (red or purple in sect. Rubro-Empetrum vs. black in sect. Empetrum), but also on, e.g., leaf shape and surface and shoot pubescence. Differences in ploidy levels and sex relationships are partly recognized. Diploids are reported to have unisexual flowers and tetraploids hermaphroditic ones but there are exceptions. Vassiljev's system has been adopted, partly or entirely, in several Russian treatments (e.g., Tzvelev 1980d for the Russian Arctic; Tzvelev 1991b for the Russian Far East). Kuvaev et al. (1996) accepted Vassiljev's main northern Russian and Siberian taxa but recombined them as subspecies of E. nigrum. Baikov (1996b) did not apply Vassiljev's system for Flora Sibiri. Vassiljev's system has not been adopted outside Russia. We (Murray and Elven) tried to apply Vassiljev's criteria and key to northwestern North American plants without success.
Authors outside Russia have considered the genus differently. Some have treated it as monotypic, i.e., consisting of E. nigrum only. The majority have accepted at least two species: the Southern Hemisphere E. rubrum Vahl ex Willd. and the Northern Hemisphere E. nigrum. And many authors have accepted in addition the (northern) species or subspecies E. hermaphroditum and E. eamesii. Anderberg (1994) proposed a rough phylogeny for the genus based on morphology and applying Vassiljev's taxa. He found support for a division between the Southern and Northern Hemisphere plants but not for Vassiljev's hypothesis of a close relationship between red and purple-fruited northern plants and red-fruited southern plant(s).
Two molecular studies throw some light on the variation but do not resolve the genus very well: Mirré (2004), based on AFLP markers and morphology, and Popp et al. (in prep. a, b), based on plastid trnS-trnfM and trnS-trnG and nuclear RPB2 and RPC2 sequences, in addition to the AFLP results. Both studies utilize flow cytometry data to identify ploidy levels. The results are applied in the treatment by Murray et al. (2009) and in this Chekclist and can be summarized as follows:
In the Northern Hemisphere, two major groups are identified: a diploid, northeastern American E. eamesii with translucent pink to red fruits and a diploid, triploid, and tetraploid, boreal to arctic circumpolar E. nigrum s. lat. with opaque, black fruits. A tetraploid northeastern American E. atropurpureum with opaque purple fruits is supported as an allotetraploid from E. eamesii and diploid E. nigrum. The diploid Southern Hemisphere E. rubrum is recognized and seems to have its closest molecular connection with and to have derived fairly recently from northwestern (Pacific) North American black-fruited E. nigrum s. lat. (Popp et al. in prep. b).
The variation within E. nigrum s. lat. was not resolved. Diploids (assumed or documented to be dioecious) are found in temperate-boreal Europe (E. nigrum s. str.), Siberia, temperate-boreal northeastern North America (see Murray et al. 2009: 487), and in the Pacific regions at least in western North America north to Alaska (Mirré 2004; Popp et al. in prep. a). Tetraploids (assumed or documented to be hermaphroditic) are found at high altitudes and latitudes throughout and perhaps as predominant in Asia. Tetraploids seem to have arisen several times from different combinations of diploids and cannot be assigned to a single lineage or taxon. The name E. hermaphroditum is based on tetraploid Greenland plants but these differ in molecular markers from the tetraploids in Europe and northwestern North America. The name should therefore not be applied generally to the tetraploid level as this level probably is highly polyphyletic. We refrain from recognizing races within E. nigrum s. lat.
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Empetrum nigrum (Tatra Mountains, Grze?)
Source: Selso at Wikispecies
