(White mountain-avens)
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Photo of Dryas octopetala by Adolph Murie
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The most widespread and abundant alpine tundra species in the northern part of Denali, white mountain-avens is a low-growing dwarf shrub with leathery leaves and parabolic eight-petalled white flowers with usually 8 petals and 8-10
sepals. Plants grow 2-12 cm tall from prostrate, branching woody stems forming dense mats with many persistent dead leaves remaining on the branches. Leaves are leathery,
oblong-
elliptic, and
crenate margined to
toothed, the margin in-rolled, dark green on the upper surface, white-hairy below. The midvein on the underside of the leaf has characteristic reddish scales with a tuft of long white hairs, distinctive to the species, known as 'octopetala scales', and visible with a hand lens. Flowers grow on leafless stalks which are also white-hairy.
Sepals are white-hairy, also with black
glandular hairs. Fruits are single-seeded
achenes with long feathery
styles, the
styles twisted together early in fall before opening into a dandelion-like head. The rusty brown scales on the midvein of the leaf distinguish this species from other mountain-avens in the park, though hybrids are known to occur.
White mountain avens is a long-lived, perennial species. It produces new flower buds in the fall, which over-winter. Leaves are semi-evergreen.
Dryas octopetala produces new leaves the whole growing season, and at the same time, the oldest leaves senesce. Leaves overwinter, as such, an individual plant always has many different ages of leaves together (
Jonasson 1989). It usually flowers in early summer.
A
monoecious species, with bisexual flowers that are obligately cross-pollinated in Alaska. Its relationship to
D. alaskensis is complex, see that species.
D. octopetala also grows clonally, forming large mats.
Dryas octopetala is an incompletely circumpolar arctic-alpine species complex, occurring from the European alpine-arctic through Japan and Siberia to Alaska and further east. In North America, this species ranges from Alaska south to Colorado and Utah in the Rocky Mountains, and eastward across Yukon and Northwest territory to the Canadian Arctic Archipelago. In Alaska, D. octopetala occurs in the alpine regions and arctic slope, and on the western coast, rare in the southern coastal mountains and southeast Alaska Southeast. In Denali, it is abundant in the alpine, particularly north of the Alaska Range. Dryas octopetala also occurs on the south side of the Alaska Range crest along Broad Pass and slopes near the Yentna River.
Details are shown in the Plots & Charts found at right, depicting recent Denali data.
This species has the widest elevational range of all the Dryas species: occurring from 275-1753 m. It occurs on all slopes, most frequently on 20-28 degrees. It occurs with near equal frequency on all aspects, but has the highest cover on south-facing slopes. White mountain avens is most abundant at high elevations (> 1100 m).
Details are shown in the Plots & Charts found at right. For more on how to interpret these figures, visit Understanding Data Presented.
Well-drained dry to moist sites.
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