Acomastylis rossii (R. Br.) Greene
Rosaceae, rose family.
Leaf. 1: 174. 1906.
Sieversia rossii R. Br. Chlor. Melvil. 18. 1823.
Geum
rossii (R. Br.) Ser. in DC. Prodr. 2: 553. 1825.
Vegetative morphology. Plants perennial herbs; 20–40 cm high; caespitose; with a rosette of interruptedly pinnate leaves with about 7 pairs of variously toothed leaflets. Taproot present. Caudex present (very stout, sub-ligneous, covered with the marcescent remains of old leaf-bases). Ground-level or under-ground stems horizontal, or vertical and often branched (orientation of the stem appears to vary with substrate); rhizomatous; elongate; 2–20 mm wide. Rhizome from which leaves arise; aerial stems erect, or ascending. Leaves in a basal tuft; alternate (in a basal rosette); compound; existing for a single season or less and marcescent (leaf blades deciduous; petioles and stipules marcescent). Stipules present; scale-like; (7–)8–12 mm long; 2.5–3.5 mm wide; brown, or pink or reddish. Stipules glabrous. Stipules apex acute (fused to the base of the petiole). Petioles 20–35(–50) mm long (further south); glabrous. Blades 20–30(–40) mm long; 8–15(–20) mm wide. Blades veins palmate (leaflet veins pinnate). Blades adaxial surface glabrous (on blade surfaces), or hairy (on the margins). Blades abaxial surface dull; glabrous (on blade surfaces), or hairy (on the margins). Blades abaxial surface hairs white, or translucent hairs (if applicable); spreading. Blade margins serrate, or entire (smaller blade divisions); with non-glandular hairs; with teeth toward the apex; degree of incision 70–80 % (major incisions, minor incisions commonly 10–50%); with teeth on each side of the blade 2, or 1 (small arctic plants). Leaf apices acute, or obtuse. Leaflet arrangement pinnate. Leaflets 12–16; 7–15 mm long; 2–4(–5) mm wide; oblong. Leaflets veins conspicuous. Apical leaflet base not distinctly stipitate.
Reproductive morphology. Flowering stems present. Flowering stems conspicuously taller than the leaves; with leaves; hairy. Flowering stem hairs woolly; simple (and), or glandular; shorter than the diameter of the flowering stem, or longer than the diameter of the flowering stem; white or translucent. Flowers solitary (usually in the Arctic), or in inflorescences (with two flowers, further south). Inflorescence diffuse (if applicable); elongating as the fruit matures. Pedicels absent (usually), or present (if in inflorescences). Flowers per inflorescence 1 (usually), or 2–3; medium-sized, 5–15 mm in diameter or length (arctic), or large, more than 15 mm in diameter or length (warmer habitats). Calyx sepals 7–10; free; 4.5–7 mm long; 1.5–3 mm wide. Calyx green; hairy; hairs long-silky. Calyx hairs white or translucent. Petals free; 5–7; yellow; obovate (to almost circular); unlobed; (5–)8–10(–15) mm long; 7–10 mm wide. Stamens 30–50(–60); filaments glabrous. Anthers yellow; subglobose; 0.4–0.6 mm long. Gynoecia superior. Carpels apocarpous; 10–30(–50). Styles 2–6 mm long. Styles conical; basal portion with hairs at the base. Stigmas receptive surface at the end of an otherwise unmodified style. Fruit with calyx persisting; dry; an aggregate of nutlets; ovoid; indehiscent. Fruit 3–4 mm long; 7–9 mm wide (individual nutlets 2–2.5 mm long, excluding the style; 0.4–0.6 mm wide, covered in upward pointing hairs); brown; hairy; surface appearing veinless.
Chromosome information. 2n = 56 (1 count), 70 (2 counts).
2n = 56 (8x). - Gajewski (1957); Wiens and Halleck (1962
western North America); Mosquin and Hayley (1966 northern Canada,
2n =
c. 56); Zhukova (1967, 1969 north eastern Asia); Zhukova and Petrovsky (1976,
1987a north eastern Asia).
70 (10x). - Zhukova (1966, 1967,
1969 north eastern Asia); Mulligan and Porsild (1969b); Löve et al. (1971
western North America); Zhukova and Tikhonova (1971, 1973 Chukotka); Zhukova et
al. (1973 north eastern Asia); Dawe and Murray (1979 Alaska); Zhukova and
Petrovsky (1980, 1987a north eastern Asia). Ploidy levels recorded 8x&10x.
Distribution. Northern hemisphere distribution: amphi-Beringian (with widely disjunct collections from Melville and Ellesmere); Canada, United States. Low arctic, or alpine. Range in the Canadian Arctic Archipelago limited. Uncommon. Arctic Islands: Ellesmere, Axel Heiberg, Parry Islands (Bathurst andMelville).
Ecology and habitat. Substrates: wet meadows (occasionally, e.g. CAN 268168, 320126), tundra, slopes (gentle or flat); imperfectly drained moist areas, or on seepage slopes, or on solifluction slopes, or dry (rarely, e.g. CAN 342945); calcareous; rocks, clay; with low organic content.
Notes. Hebda and Chinnappa (1990) reported that the pollen of this
taxon is produced in monads that are isopolar, radially symmetrical, and
tetracolporate. The grains are subspheroidal to subprolate with a circular to
subtriangular amb. They have a well-developed chambered aperture formed by
overarching pore flaps. Flaps extend over the aperture but do not join to form
an equatorial bridge. Exine is tectate, microperforate, with a thin nexine.
Sculpturing is striate or occasionally rugulate and consists of ridges and
valleys with microperforations on valley floors. Ridges and valleys are oriented
predominantly parallel to the colpus but occasionally curve or loop near the
poles.
Chambers et al. (1990) observed the effects of disturbance type on
seedling environment and establishment of alpine species with different
physiological and life history traits during a 2-yr study on the Beartooth
Plateau in southwestern Montana, USA. They compared soil temperatures, water
potentials, and nutrients on mineral soils of a gravel borrow area with those on
highly organic soils of a Geum turf area. Seedling emergence, growth, and
survival of six seeded species (Geum rossii, Artemisia scopulorum,
Potentilla diversifolia, Sibbaldia procumbens, Deschampsia
cespitosa, and Festuca idahoensis) and emergence and survival of five
unseeded species (Draba crassifolia, Draba incerta, Cerastium aryense,
Arenaria rubella, and Androsace septentrionalis) were evaluated on
both areas. The effects of N and P nutrient addition and surface organic mulch
on the soil environment and seedling establishment were evaluated on the borrow
area, while differences between uncleared turf and turf cleared of vegetation
were compared on the Geum turf area. Plots cleared of vegetation on the
Geum turf area had higher levels of soil N (NO3-) and P than uncleared
turf and both higher levels of N (NO3- + NH4+) and P and higher soil
temperatures (surface, 5, and 15 cm depths) than fertilized or not-fertilized
borrow area treatments. Fertilization increased N and P on borrow area soils,
but after 2 yr N had decreased significantly. Soil water potentials (5 and 15 cm
depths) did not differ between cleared plots on the Geum turf area or any
of the borrow area treatments and were never low enough to cause plant stress.
Vegetated Geum turf had significantly lower water potentials than cleared
plots, especially late in the growing season. Mulch had no effect on soil water
potential or nutrients on the borrow area and increased soil temperatures only
on clear days during the first growing season. Wind removed or redistributed the
mulch over time, thus decreasing potential effects. Seedling emergence was
highly dependent on soil surface stabilization and reflected species life
history traits. Growth of seedlings was slow, and varied among species and
treatments: 0.005–0.04 and 0.02–0.20 g total mass after the first and
second growing seasons, respectively. Significantly higher total seedling mass
was observed on cleared Geum turf plots than on any of the borrow area
treatments, and on fertilized than on not-fertilized plots on the borrow area.
Seedling mortality of most species was much lower than previously found for
alpine ecosystems, rarely exceeding 50% even after 2 yr. On the borrow area
mulch increased survival, probably through microenvironmental amelioration. The
nutrient pulse from fertilization increased mortality of several species,
presumably by creating plant nutrient demands in excess of availability during
year 2. Both disturbance characteristics and species life history and
physiological traits affected seedling establishment. Pretreatment soil
properties of the two disturbance types had the greatest effects on soil
temperatures and nutrients and, consequently, on seedling growth and survival.
Soil surface characteristics had the largest effects on seedling emergence;
surface stabilization was essential for holding both soil and seed in place.
Single species responses varied in magnitude but were similar on both
disturbance types. In general, there were larger differences among species in
emergence and growth than in survival. Thus, successful seedling establishment
on different alpine disturbance types may depend more on obtaining the necessary
conditions for seedling emergence and on species interactions than on the
ability of seedlings to survive different environmental conditions.
Chambers
(1991) studied the relationships of clone area and neighborhood to ramet size,
reproductive effort, and spatial distribution within Geum rossii clones
in an alpine ecosystem on the Beartooth Plateau, Montana [USA]. Clones growing
on an early seral site in relative isolation were compared to clones on a late
seral site within dense, heterogeneous neighborhoods. Individual clones of G.
rossii required a minimum clone area of about 200 cm2 before maximum ramet
size and reproductive effort were achieved. Mean ramet size and reproductive
effort were fairly constant among clones larger than 200 cm2 on both the early
and later seral sites. Within clones the size and reproductive effort of ramets
were positively related. Pattern analysis revealed that ramets became more
widely and irregularly spaced as clone area increased on the early seral site.
This may have been a geometric function of an increase in the space required as
clones aged and became larger. On the late seral site, clones were characterized
by ramets that were widely and erratically spaced, that had low leaf numbers and
mass, and that had low reproductive effort. For clones of comparable area on the
early seral site, ramets were more closely and uniformly spaced, and leaf
number, mass, and reproduction per ramet were higher. Conservative patterns of
growth and reproduction make G. rossii well suited to dominate in dense,
heterogeneous neighborhoods of late seral sites and to colonize mineral soils of
early seral sites. Similar to other clonal species, site characteristics and the
type of neighborhood determine the trade-off between the physical occupation of
space and the allocation to ramet growth and reproduction in G. rossii.
Illustrations. • Close-up of plant. Plant in flowering stage. Alaska: Seward Pen., Mt Distin. July 1998. Photographed by R.Elven. Voucher in HbO. • Close-up of leaf and flower from side. Turn 90 degrees clockwise.. Leaf showing the irregular pinnae. Flower sidewise showing episepals and sepals. Alaska: Seward Pen., Kigluaik Mts, Anfield Creek. Aug. 2001. Photographed by Heidi Solstad. Voucher in HbO. • Close-up of flower. Flower showing stamens and carpels. Alaska: Seward Pen., Kigluaik Mts, Anfield Creek. Aug. 2001. Photographed by Heidi Solstad. Voucher in HbO. • Close-up of plant. Plants with shiny, glabrous, pinnately compound leaves and flowers with yellow petals. Alaska, Lake Peters, July 13, 1961. CMN Photo library S78–634, photograph by Raymond Wood. • Arctic Island distribution.
Cite this publication as: ‘S.G. Aiken, M.J. Dallwitz, L.L. Consaul, C.L. McJannet, L.J. Gillespie, R.L. Boles, G.W. Argus, J.M. Gillett, P.J. Scott, R. Elven, M.C. LeBlanc, A.K. Brysting and H. Solstad. 1999 onwards. Flora of the Canadian Arctic Archipelago: Descriptions, Illustrations, Identification, and Information Retrieval. Version: 29th April 2003. http://www.mun.ca/biology/delta/arcticf/’. Dallwitz (1980) and Dallwitz, Paine and Zurcher (1993, 1995, 2000) should also be cited (see References).
