BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Selaginella densa | Little Clubmoss 



GENERAL BOTANICAL CHARACTERISTICS : 
Description:  Little clubmoss is an evergreen, nonflowering herb that
forms dense, cushionlike mats which are seldom more than 1 inch (2.5 cm)
in height [10,57].  The short, leafy, compactly branched stems lie along
the soil surface and may be 4 inches (1 dm) across [27].  The simple,
awn-tipped leaves are very small, up to about 0.1 inch (2.5 mm) long and
0.02 inch (0.5 mm) wide, and arranged in a relatively dense spiral along
the stem.  There is usually a single, unbranched vein.  The leaves
underneath the stem are longer than leaves on top along the same part of
the stem [42].  Little clubmoss has true roots which are very fine
(0.008 inch or 0.2 mm in diameter) and minutely branched.  They form a
tangled mass and may comprise 86 percent of the plant dry matter [59].
Most roots occur within 0.78 to 2.0 inches (2-5 cm) of the soil surface
[12].

Drought Resistance:  Little clubmoss is very resistant to drought if the
roots are not disturbed.  In the laboratory, clumps allowed to dessicate
for 6 and 33 months were then revived simply by watering and later
planting [55,61].  The clump that was revived after 33 months developed
reproductive cones within 3 months [61].  When all soil was removed from
roots, no plants survived after 5 weeks of air drying [59].  Shoots that
are dormant during drought have their leaves closly appressed to the
stem and are a dull grayish-green instead of the ash-gray of dead shoots
[61].  Young plants are equally drought resistant.  On a site near
Saskatoon, Saskatchewan, Webster and Steeves [61] found over 50
locations where sporelings had survived periods of drought.


RAUNKIAER LIFE FORM : 
   Undisturbed State:  Chamaephyte
   Burned or Clipped State:  Chamaephyte


REGENERATION PROCESSES : 
The clubmoss life cycle differs from that of flowering plants.  At
branch ends, four-angled "cones" or strobili are formed.  Each has two
types of spore-bearing structures, microsporangia and megasporangia, in
the leaf axils, with megasporangia located below the microsporangia
[61].  Microspores are released passively to fall through the strobili
to the ground [32].  At maturity they will release microscopic,
flagulated sperm cells.  The sperm require water to swim to the egg cell
which develops from cells of the megasporangia.  Where fertilization
occurs is not known [52].  Tissue surrounding the fertilized egg may
carry on photosynthesis as well as provide stored food for the
developing embryo.  This entire structure may be shed or held in the
leaf axils of the strobili while the embryo develops.  The necessity of
water for sexual reproduction restricts the habitat of clubmosses [15],
and young plants are not often reported [18,52].

As little clubmoss clumps grow the centers die, leaving a ring of live
material surrounding a dead core [59].  Under range conditions lateral
growth was observed to be less than 0.4 inch (1 cm) a year, making
vegetative spreading a slow process [18,59].  During another field study
growth of less than 0.2 inch (5 mm) in 5 seasons was observed [52].
Fragmentation might be another means of vegetative reproduction and
dispersal [18], although stems of little clubmoss do not have a natural
tendency to fragment when dry [55].


SITE CHARACTERISTICS : 
Little clubmoss is most often found on dry shallow soils that are
gravelly or rocky or have gravelly or stony subsoils [57].  It is most
common in grasslands, alpine tundra, and high subalpine communities
which occupy dry, snow-free ridges.  Little clubmoss is an extremely
stress-tolerant species and can survive in cold alpine regions with a
short growing season, drought, and summer frosts [62].  Little clubmoss
is not common in forests but can be found in Douglas-fir (Pseudotsuga
menziesii) with ponderosa pine (Pinus ponderosa) or lodgepole pine (P.
contorta), Engelmann spruce (Picea engelmannii) and subalpine fir (Abies
lasiocarpa), or aspen (Populus tremuloides) communities [33,44].  Little
clubmoss also grows in pinyon (Pinus edulis)-juniper (Juniperus spp.),
sagebrush (Artemisia spp.), and krummholz communities [63].  In Jackson
Hole, Wyoming the big sagebrush (A. tridentata) community has abundant
little clubmoss [47].  In northern Montana aspen grove and grassland
communities, it is found primarily with Hood's phlox (Phlox hoodii) on
stony moraine summits, outwash fans and coarse gravels [38].  The
abundance of little clubmoss in the aspen grove and grassland community
decreases to the north in Saskatchewan [11].

Grassland Sites:  Little clubmoss is most abundant in short-grass
prairie.  Its basal area may be equal to that of all other herbs and
shrubs [7,9].  In mixed prairie, little clubmoss is slightly less
abundant, occurring with an overall frequency of 74 to 98 percent and
cover up to 25 percent [10].  It has much less cover and is not evenly
distributed in the fescue prairie [7,11].  In the northern Red River
Valley, it dominates with needle-and-thread grass [45].  On sites with
standing surface water, little clubmoss will be unimportant [64].
However, in Montana, areas where it grows are closer to permanent water
than areas where it does not grow [57].  In North Dakota, little
clubmoss is common on a variety of grassland habitat types except those
with extra moisture [64].

Alpine and subalpine sites:  In the Washington and British Columbia
Cascades, little clubmoss is common in herbfield, the Bellard
alpinesedge (Kobresia myosuroides), and purple reedgrass (Calamagrostis
purpurascens) communities on sites that are essentially snow-free during
the winter.  On such sites it is exposed to high wind, low temperatures,
and frequent frosts all winter [20].  On alpine sites in Montana, little
clubmoss does well where Hooker mountainavens (Dryas octopetala) is
dominant [2].  In alpine areas in Utah, it grows in cushion plant
communities with alpine avens (Geum rossii) and on dry meadows and
alpine turf [37].  On the Colorado Front Range, little clubmoss is part
of several forest communities, but its greatest abundance is at higher
elevations in Bellard alpinesedge meadows or under limber pine (Pinus
flexilis) on exposed rocky sites [33,44].  It is well adapted to these
and other alpine cushion-plant communities [62].  In contrast, near
Schoolroom Glacier in the Teton Range of Wyoming, it is found in a
meadow community with kentrophyta milkvetch (Astragalus kentrophyta)
[53].  In Alberta it grows under limber pine on the rocky, dry slopes
and summits of exposed ridges [41].  In northern California little
clubmoss (var. scopulorum) grows on open rocky sites in red fir (Abies
magnifica) and lodgepole pine forests of Siskiyou County [42].

Parent material:  Little clubmoss grows in the drier interior of British
Columbia except for a disjunct population on dry, well-aerated and warm
limestone soils on the Queen Charlotte Islands [49].  In Montana, little
clubmoss does well on sites with thin, rocky, and unstable soils derived
from calcareous parent material [2].  In the Bighorn Mountains of
Wyoming, it is present on granitic soils but almost absent on soils
derived from sedimentary rock [57].

Soil texture:  Little clubmoss is common on medium texture soils and
sandy loams.  It is less common on sandy soils and rare on clay
[10,52,57].  In grasslands dominated by bluebunch wheatgrass
(Pseudoroegneria spicata) little clubmoss is found in areas with
shallower, rockier,and less sandy soils than areas without little
clubmoss [57].  Optimum soil depth for little clubmoss (var. densa) is
between 10 and 20 inches (25.4-50.8 cm) [16].  Growth of little clubmoss
(var. densa) on various soils in several western states is ranked as
follows [16]:

                      UT       WY       MT       ND
Soil texture
  Gravel             good     fair     fair     fair
  Sand               good     poor     fair     fair
  Sandy loam         good     good     fair     fair
  Loam               good     good     good     good
  Clay loam          good     good     good     good
  clay               fair     fair     fair     good
  dense clay         poor     poor     poor     poor
Organic soils        fair     poor     poor     ----
Acidic soils         fair     poor     poor     ----
Saline soils         fair     poor     poor     poor
Sodic soils          ----     poor     poor     fair
Sodic-saline soils   poor     poor     poor     poor

Elevation:  Elevational ranges in some western regions are
[16,26,30,42,63]:

                     Minimum                   Maximum
                    feet     meters          feet     meters

Arizona            11,470    3,496         11,470     3,496
California
 var. scopulorum    5,000    1,524          7,000     2,134
Colorado
 var. densa         4,000    1,219         12,000     3,658
 var. scopulorum    8,000    2,438         12,500     3,810
 var. standleyi     9,500    2,896         13,000     3,962
Montana            
 var. scopulorum    6,300    1,920          6,300     1,920
Utah                8,858    2,700         14,107     4,300
Wyoming
 var. densa         6,000    1,829         10,800     3,292
 var. scopulorum    5,600    1,707         10,800     3,292
 var. standleyi     5,600    1,707         10,800     3,292


SUCCESSIONAL STATUS : 
In general, clubmosses (Selaginella spp.) are unable to compete with
other plants in relatively moist habitats [55].  They also are not
important pioneers.  Instead clubmosses are found on open, xeric sites
supporting particular plant communities but shift locally within those
communities.  On such open sites their ability to withstand desiccation
allows them to survive and grow well [55].  On alpine sites of Montana's
Beartooth Plateau, little clubmoss pioneers on the gravel mulch left by
rodent disturbance in grassy meadows [29].  Little clubmoss (var.
scopulorum) is found in alpine areas on unstable soils disturbed by
frost and abraided by wind [29].


SEASONAL DEVELOPMENT : 
In North Dakota spore production begins in June and finishes in July
[16].  In Canadian mixed prairie, vegetative growth begins in early
April, strobili first appear late in April, and spores mature late in
May [10].  In the Colorado alpine, leaves of little clubmoss remain
green all winter when protected from wind but turn brown and erode where
exposed [3].  The cones (strobili) change from green to brown in late
May or early June when they are released from snow [3].  

Related categories for Species: Selaginella densa | Little Clubmoss