(Alaskan mountain-avens)
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Photo of Dryas alaskensis by Carl Roland
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Alaska mountain-avens is a dwarf-shrub (woody but prostrate) forming dense, low mats in alpine tundra, meadows and snowbed areas, also occurring in isolated open patches in subalpine shrub tundra. Patches of Alaska mountain-avens are dotted with large white to cream flowers. Dryas is easily distinguished from any other genus, but identifying one to species relies on minute hair and gland characters of the leaves.
Plants grow from prostrate woody stems, underlain by persistent dead leaves, and leafless stems with single flowers. The leaves are oblong to lanceolate, 0.8-4 cm long, quite leathery, dark green above, green-gray below. Leaf margins are inrolled, and the underside is short hairy. The leaf midvein on the underside has gland tipped hairs (rarely hairless), a distinguishing character of the species. The crenate leaves are 2.5-3.5 times longer than broad.
Flowers have eight white petals, many yellow stamens and greenish pistils, the whole blossom 2-3 cm across. Petals are broadly elliptic, and the flower is broadly cup-shaped. The flowering stem is white hairy and supports 8-10 sepals, which are brownish and with white hair and glandular hairs.
Its fruits are a group of unfused achenes, attached to long styles covered in feathery white hairs, to facilitate wind dispersal. The styles are twisted together when the fruits develop, opening into a dandelion-like head in maturity.
To help distinguish this species from the more common and widespread D. octopetala, it should be noted that D. alaskensis' leaves are longer and more oblong, and without the rusty-colored scales with tufts of white hair on the leaf midveins. Hybrids between D. alaskensis and D. octopetala are known to occur and have intermediate leaf morphology. Don't be too discouraged if you can't tell the species of Dryas apart - sometimes it is difficult for experienced botanists as well, so just enjoy their beauty.
Dryas alaskensis is perennial, and the leaves overwinter. It is a snowbed species, flowering as soon as the snow melts. This leads to a later blooming time than D. octopetala.
Dryas alaskensis is a
monoecious species with bisexual flowers. Alaska mountain avens is exclusively out-crossing, not self-fertile or
apomictic (
McGraw and Antonovics 1983;
Max et al. 1999). The species is inter-fertile with
D. octopetala, and many authors treat
D. alaskensis as a subspecies. Seeds have long plumes (persistant
styles), allowing them to be wind dispersed. Seeds require brief cold stratification and mimicry of Alaskan spring temperatures in order to germinate. Experiments on Alaska seeds yielded high germination rates (
McGraw and Antonovics 1983). A study by
Max et al. (1999) germinated seeds from naturally pollinated flowers from central Alaska. They found little genetic differentiation between
D. octopetala and
D. alaskensis, but consistent morphological distinction between the two (
Max et al. 1999). Because
D. alaskensis flowers at a different time than
D. octopetala, natural hybridization is improbable (
McGraw and Antonovics 1983). However, 14% of the seeds germinated by Max et al. from natural populations had different morphology in glands and scales then their parent plant—indicating either there is gene flow between the two, or that these characters are not restricted to each species.
Dryas also grows clonally, forming large mats.
Alaska mountain avens is an amphi-Beringian endemic species. In Alaska, Alaska mountain avens occurs in the Brooks Range, the Seward Peninsula, uplands in the Interior and southwest, the Alaska Range and Wrangell Mountains. It is known from adjacent alpine Yukon, and a few collections have been made of the species in Chukotka. In Denali, the species is common and widespread in alpine areas on north of the Alaska Range crest, and occurs in the northern Chulitna River drainage on the south side of the range.
Details are shown in the Plots & Charts found at right, depicting recent Denali data.
Alaska mountain avens is an alpine species preferring steep, north-facing slopes. It has the highest degree of cover on moderately steep slopes (20-28) degrees (close to 2% cover). Additionally, the cover of sites sampled above 1100 meters is close to 2%, and it occurs in over a quarter of all such plots. This species grows in a fairly narrow range of elevations, not found below 769 m. This species relationship with aspect is equally strong: cover on south-facing slopes is less than 0.25%, and it dramatically increases on north-facing plots, reaching 1-1.75% cover. It is the second most abundant Dryas species in the Park.
Details are shown in the Plots & Charts found at right. For more on how to interpret these figures, visit Understanding Data Presented.
Alaska mountain avens grows on gravelly slopes.
Wide-ranging, occurs in somewhat wet to well-drained sites.
