BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Drosera rotundifolia | Round-Leaved Sundew 



GENERAL BOTANICAL CHARACTERISTICS : 
Round-leaved sundew is an insectivorous, short-lived perennial forb
arising from a basal rosette of leaves.  The upper surface of the leaf
blades are covered with reddish, glandular hairs tipped with a sticky,
glutinous secretion that traps insects.  The inflorescence is a
one-sided raceme with 2 to 15 flowers on a scape that is 2 to 10 inches
(5-25 cm) long.  There may be one to seven inflorescences per rosette.
The fruits are capsules with numerous small seeds [8,20,21,41,44].

The root system of round-leaved sundew is usually shallow (less than 2.4
inches [6 cm]) [8].  It consists of a taproot - functional for less than
a year - which is replaced by mostly horizontal adventitious roots with
a few root hairs [8,37,50].

Round-leaved sundew compensates for the low available nutrients in its
habitat by catching and digesting insects [8,45,49,54].  Insects are
caught with the sticky glandular leaf hairs, and the leaf then folds
around the prey.  The hairs secrete proteolytic enzymes which digest the
insect and enable the plant to absorb nutrients through its leaves
[37,45,52].  Insect capture is generally believed to enhance growth and
reproduction of round-leaved sundew [8,24,29,46,56].  It is
significantly correlated (p<0.01) with total leaf number, number of new
leaves formed, and total leaf area [46].  However, Stewart [50]
determined that round-leaved sundew did not benefit from insect capture
in field experiments in the Jefferson National Forest, Virginia.  The
benefits of insectivory may be site-dependent; round-leaved sundew may
benefit most from insect capture on the most nutrient-poor sites.




RAUNKIAER LIFE FORM : 
   Hemicryptophyte


REGENERATION PROCESSES : 
Round-leaved sundew reproduces vegetatively or by seed [8,29,37,52].
Vegetative reproduction takes place when leaf buds form plantlets, or
when axillary buds below the rosette form a secondary rosette.  As the
stem decays, the two separate [8,37].  Adventitious plants develop in
the autumn.  They occur occasionally in the field but are often present
in greenhouse experiments, possible due to a high level of humidity
[52].

When flowers are open during the day, they are cross-pollinated by wind
or insects.  Self-pollination may take place as flowers close in the
evening [45,50].  The fruits often persist unopened, and seeds are
released when the fruit rots [8].  The fusiform seeds are 0.06 to 0.07
inch (1.5-1.8 mm) long and 0.008 inch (0.2 mm) wide and have an inflated
testa.  Air trapped in the testa makes the seed buoyant and capable of
floating for days on water surfaces.  Seeds may be carried some distance
with snowmelt and flooding [52].  Plants flower in their first summer
and every year thereafter [8].


SITE CHARACTERISTICS : 
Round-leaved sundew is most often found in bogs, but also grows in
swamps, rotting logs, mossy crevices in rocks, or damp sand along
stream, lake, or pond margins [31,37,39,52,59].  It is generally
associated with sphagnum mosses and grows on floating sphagnum mats or
sphagnum hummocks [8,29,32,37,50].  It may also grow on peat soils of
other bryophyte or of graminoid origins [1].  In the northern part
of its range the sphagnum bogs in which round-leaved sundew grows are
generally found surrounding glacial lakes.  In the Appalachians from
Pennsylvania to Alabama, the bogs are most often at confluences of
springheads, around seeps, or along streams rather than lake margins.
The same is true for sphagnum bogs of the southeastern coastal plain,
but there round-leaved sundew may also grow in grass-sedge bogs.  In the
Pacific Northwest, sphagnum bogs are typically found along streams and
occasionally develop around high elevation seeps and shallow lake
margins in the northern Rocky Mountains [3,45].

Round-leaved sundew is usually confined to sites with a high water table
or high precipitation and humidity [8].  It requires continually moist
or wet situations [20].  Round-leaved sundew grows in organic acid soils
that are low in available nutrients (nitrogen and phosphorous, and
calcium [3,24,49,54].  According to Crowder [8], the normal range of the
water table on sites where round-leaved sundew grows is from 1 inch (2
cm) above to 16 inches (40 cm) below the soil surface.  Flooding can be
tolerated for several weeks, but dry periods can only be tolerated for a
very short time.  Lloyd [37] reported that it is not found on limestone
soils; high calcium concentrations may be toxic to the plant.

Round-leaved sundew grows in sedge meadow communities of the Huntingdon
Marsh in Quebec on peat underlain by clay at 24 inches (60 cm) or more.
The soil surface is slightly above or up to 10 inches (25 cm) below the
water table [2].  Round-leaved sundew has been reported as growing on
sites ranging from neutral pH (7.3) to very acidic (3.2) [18,38].
Acidic soils with low nutrient concentrations (nitrogen, phosphorous, or
calcium) seem to be the most common substrate [2,11,38,49,61].

In British Columbia, round-leaved sundew is an indicator of wet to very
wet, nitrogen-poor soils in boreal, cool temperate, and cool mesothermal
climates.  It is associated with sphagnum moss in nonforested,
semiterrestrial communities [28].

An atypical site was found on Ile Perrot, Quebec, where round-leaved
sundew was growing on moderately dry, abandoned pastureland that
originally had been a swamp.  The soil was well-drained loamy sand with
an average pH of 6.1.  The site was "basically infertile" with extremely
low calcium and nitrogen concentrations [52].


SUCCESSIONAL STATUS : 
Facultative Seral Species

Round-leaved sundew is very shade intolerant [28,50].  Since the plant
is so small, even graminoids and small shrubs may limit light
availability [50].  Shaded plants may not develop a rosette but instead
have a more spindly habit [8].  The encroachment of poison sumac,
speckled alder (Alder rugosa), and purple chokeberry (Pyrus floribunda)
into a kettle bog at Brown's Lake Bog Preserve in northeastern Ohio has
resulted in the "shading out" of characteristic bog species including
round-leaved sundew, pitcher-plant, and sphagnum mosses [12,63].  One
bog in Jefferson National Forest, Virginia, is kept in an early
secondary successional stage by periodic removal of ferns (Osmunda
spp.), alders, and other shade-producing plants.  This treatment has
resulted in a proliferation of sundews (Drosera spp.)  [50].

The adaptations of round-leaved sundew to nutrient-poor conditions
allows it to be very competitive and persistent in acid wetlands [45].
It has invaded disturbed sites in bogs after peat mining, ditching, and
burning [8,37,45,52].  In subarctic Manitoba, round-leaved sundew was
present in undisturbed bogs and in a bog that had been completely
cleared of vegetation 7 years earlier [48].  However, if succession
leads to the invasion of bogs by woody vegetation, round-leaved sundew
is easily shaded out as site conditions are altered [45].  In rich fens
round-leaved sundew is probably at a competitive disadvantage because of
higher species diversity [24,50].

Bog succession in general is not well understood [3,24].  Bogs can be
formed by the filling-in of lakes or ponds, or the paludification
process where forests are converted to wetlands [24].  Many bogs are
apparently stable and very long-lived, whereas others are ephemeral
unless frequently disturbed [3].  On Isle Royale in Lake Superior,
round-leaved sundew was present in mid-seral stages of succession from
rocky shore to forest and was also seral in bog succession, occurring
mostly between aquatic stages and bog forest [6,7].  The same general
pattern describes the role of round-leaved sundew throughout peat bogs
in eastern North America [9].



SEASONAL DEVELOPMENT : 
Round-leaved sundew generally flowers from June to September throughout
its range [19,30,39,45].  Flowers open one per day, starting from the
bottom of the inflorescence [50].  Seed dispersal begins in July and
most seeds fall before winter.  However, some may be found in dried
capsules in the spring [8].  Round-leaved sundew forms a hibernaculum
(tightly rolled leaf primordia) in the fall.  The remaining leaves, and
frequently the roots, die back after the hibernaculum develops.  The
hibernaculum opens in April or May of the following year [45,55,62].

Related categories for Species: Drosera rotundifolia | Round-Leaved Sundew