Panarctic Flora

672118 Draba lactea Adams

• Adams, Mém. Soc. Imp. Naturalistes Moscou 5: 104 (1817). Lectotype (MW!): Siberia: the Lena River estuary, "ad mar. glac., leg. Adams (scripsit) 4856, herb. Hoffm. (Berkutenko 1979: 120).
• Draba wahlenbergii Hartm., Handb. Skand. Fl.: 249 (1820). Described from Scandinavia. No type designated.
• Draba pseudopilosa Pohle, Izv. Imp. Bot. Sada Petra Velikago 14: 469 (1914). Described from the Lena River estuary in Yakutia (Siberia). Berkutenko (1979) identified four syntypes (LE!) but did not designate a lectotype.
• Draba allenii Fernald, Rhodora 36: 289 (1934). Holotype (GH): Canada: Quebec, Mount Mattaouisse, south side of Fernald Pass, 08. July 1923, leg. Fernald et al. 25,799.
• Draba boecheri Gjærev. & Ryvarden, Kongel. Norske Vidensk. Selsk. Skr. (Trondheim) 1977, 4: 23 (1978) "böcheri". Holotype (TRH!): Greenland: "Jensens Nunatakker, Hornblenderyggen (nordsiden)", 31. July - 07. Aug. 1967, leg O. Gjærevoll and L. Ryvarden.

2n= (1) 32 (4x). - Siberia (N), Far East (N), Alaska, Greenland. - Three reports, partly for D. pseudopilosa (Siberia, Far East). Tetraploid in FCM, Grundt et al. (2005b; western Alaska, Greenland).
(2) 48 (6x). - Europe (N), Siberia (N), Far East (N), Alaska, Canada, Greenland. - Numerous reports, partly for D. pseudopilosa. Hexaploid in FCM, Grundt et al. (2005b; Norway, Svalbard, Siberia, Alaska, Canada, Greenland).
Not included: A report of 2n = 16 (2x) from central Alaska (Dawe and Murray 1981c) was based on a subglabrous form of D. nivalis (voucher specimen in ALA inspected by Elven, Grundt, and Murray). For a report of 2n = 24 (3x) from southwestern Greenland (Böcher in Gjærevoll and Ryvarden 1978, as D. "böcheri"), see notes below.

Geography: Circumpolar: NOR RUS SIB RFE ALA CAN GRL.

Notes: Grundt, Petrovsky, and Elven: There are numerous reports of Draba lactea from Iceland but all specimens we have inspected (AMNH, C, ICEL, O) belong to the polymorphic D. rupestris.

The diagnosis of Adams (1817) was ambiguous and the original material from the Lena River estuary includes two species: D. lactea as currently considered (specimens in MW! and G-DC!) and D. fladnizensis (specimens in LE!). Berkutenko (1979) designated a MW specimen as lectotype (inspected by Elven and Solstad in 2003) conforming to our current view of the species.

Draba lactea is genetically allopolyploid as suggested by, e.g., Knaben (1966) and documented with fixed heterozygosity by Brochmann et al. (1992). Knaben and others proposed an origin from the diploids D. fladnizensis and D. nivalis. The current evidence (Grundt et al. 2004) rather points to an origin from the diploid and tetraploid Beringian D. palanderiana, i.e., taxonomic autopolyploidy at least as long as the two ploidy levels within D. palanderiana are considered within one species. The reports of delimitation problems and frequent intermediates between D. lactea and D. fladnizensis (Hultén 1945a, 1968a), and their proposed merger (Scoggan 1978c), has no foundation. The two species are consistently different both in molecular markers (Scheen et al. 1999; Grundt et al. 2004; numerous previous studies) and in morphology. Intermediates or natural hybrids have never been proven and artificial hybrids are sterile (Brochmann et al. 1993).

Draba lactea has been considered uniformly hexaploid (Knaben 1966; Löve and Löve 1975a). Tetraploids are now documented from northeastern Asia (Zhukova and Petrovsky 1984, reported as D. fladnizensis and D. pseudopilosa, see note below) and from western Alaska and eastern Greenland (Grundt et al. 2005b: FCM). The tetraploid plants from Alaska and Greenland differ slightly morphologically from the hexaploids but belong genetically within D. lactea, based on isoenzymes, RAPDs, and sequencing of two genes (Grundt et al. 2004). We include them in one species with two ploidy levels.

Four other species have been described as related to D. lactea. One (D. taimyrensis) is provisionally accepted below. We consider the three other names to be synonyms of D. lactea:

Draba allenii Fernald. - This species was described from and is reported to be restricted to northeastern Canada. Inspected specimens (CAN, DAO, S; the last one annotated as an isotype, which it is not) mostly have leaves with only simple marginal hairs (cilia) like D. fladnizensis but the vegetative structures and infrutescences are those of D. lactea. The name was considered a synonym of D. lactea by, e.g., Mulligan (1974b, comments) and Rollins (1993) and we accept their conclusions. Purely ciliate or even glabrous plants occur quite regularly in northeastern Canadian material of D. lactea and also elsewhere.

Draba boecheri ["böcheri"] Gjærev. & Ryvarden. - This species is known only from the type collections from Jensens Nunatakker in southwestern Greenland (Gjærevoll and Ryvarden 1978). The specimens on the holotype sheet deviate morphologically from the majority of the quite polymorphic D. lactea but not enough to merit rank as a different species. The two other sheets annotated as D. "böcheri" (all that ever has been collected) contain a mixture of plants of D. lactea and D. rupestris. The protologue is combined from both species and does not fit the type very well. Draba boecheri was reported with a triploid chromosome number, 2n = 24 (Böcher in Gjærevoll and Ryvarden 1978). This is most probably a mistake. Böcher cultivated the plant and may have counted the number in PMC as 24, as was his often applied technique. Gjærevoll may have assumed it to be the somatic number or used the notation of "2n" without further consideration. Ryvarden does not remember how it was done. Böcher vouchered his counts by slides but the slides are stowed away and nearly impossible to find (comment from the Copenhagen herbarium). A hexaploid number is consistent with both the relevant species: D. lactea and D. rupestris.

Draba pseudopilosa Pohle. - This species was described from the Lena River estuary, like D. lactea. Petrovsky commented that the Russian tetraploid chromosome counts originally published for D. fladnizensis (see Zhukova and Petrovsky 1984) belong to what may be local karyological races of D. pseudopilosa, and he considers this as more or less distinctly different from D. lactea. Grundt and Elven admit that D. lactea is morphologically varied in Siberia and Beringia but they see no discontinuity. Russian plants assigned to D. pseudopilosa have been compared in molecular markers with D. lactea from other areas and correspond with these (Grundt et al. 2004). Field investigations have not revealed any pronounced structure in the morphological variation in D. lactea s. lat. in northern Yakutia. The name is therefore reduced to synonymy.