BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Lolium perenne | Perennial Ryegrass 



GENERAL BOTANICAL CHARACTERISTICS : 
Perennial ryegrass is an introduced, cool-season bunchgrass that grows
up to 35 inches (90 cm) tall.  It has erect culms and short rhizomes.
Perennial ryegrass does not have a creeping growth habit [14,46].  It is
generally short-lived (2 to 3 years) [54].

Perennial ryegrass forms vesicular-arbuscular endomycorrhizal
associations [2].


RAUNKIAER LIFE FORM : 
   Hemicryptophyte
   Geophyte


REGENERATION PROCESSES : 
Perennial ryegrass is considered self-incompatible [14].  The seeds are
relatively large (0.00027 ounce [7.5 mg]), with no innate dormancy.
There are 247,000 to 330,000 seeds per pound [7,34].  The seeds tolerate
a wide range of diurnal temperature fluctuation, and germinate in either
light or darkness [18].  Casterline Seeds [7] recommended stratification
at 47 degrees Fahrenheit (8 deg C) for 5 days before planting.  This is
not consistent with most authors, who do not recognize a need for
stratification.  Perennial ryegrass seeds will germinate as soon as
moisture conditions permit, regardless of cold treatment [18,50].
Seedbanks of perennial ryegrass are limited and transient; even where
perennial ryegrass is a major component of pastures in the Netherlands,
it ranks seventh among grasses in numbers of viable seeds and does not
accumulate reserves of seeds [18,52].  Schafer and Chilcote [62]
determined that the largest decrease in buried seed is due to
germination.

This type of transient seedbanking is related to exploitation of
grasslands that are subject to seasonally predictable drought damage,
such as those of Mediterannean climates.  The lack of a persistent
seedbank explains the tendency of perennial ryegrass to be replaced by
native grasses with persistent seedbanks, especially in the more
northerly latitudes [50].

Along roadsides and in disturbed habitats in the United Kingdom,
perennial ryegrass will reproduce well from seed.  In neighboring lawns
or pastures it may be entirely dependent on vegetative reproduction
(probably because the flowering stems are removed before seed production
can occur) [18].  The success of self-seeding for stand maintenance in
the United States would appear to depend on the ability of seedlings to
establish well before frost.  Established plants are fairly winter
hardy, but since they are short-lived, recruitment from seed would be
important for stand persistence [18,49,57].


SITE CHARACTERISTICS : 
Perennial ryegrass is adapted to a wide range of soil types and drainage
conditions and can be grown successfully on earth structures such as
dams and dikes, in grass waterways, and in flood channels [14,20,57].
It does not thrive where there are extended periods of low temperatures
or drought.  Perennial ryegrass will do well in areas that are too wet
for other grasses, and short periods of flooding will not severely
reduce good stands [14,49,57].  Josselyn and others [63] listed
perennial ryegrass as a facultative wetland species (it occurs at 34 to
66 percent frequency on wetland sites in California).

Elevation occurrence data from selected western states are as follows
[9]:

             feet           meters

Utah         3,100-5,100      945-1,555
Colorado     5,000-6,500    1,524-1,981
Wyoming      3,500-6,200    1,067-1,890
Montana      3,200-7,200      975-2,195


SUCCESSIONAL STATUS : 
Obligate Initial Community Species

Perennial ryegrass is an good competitor and outcompetes other grasses
both above and below the ground [10].  Colonization of disturbed areas
and adjacent areas can take place by seed dispersal [50].  Perennial
ryegrass is probably not shade tolerant; photosynthetic capacity of leaf
bases decreases when they are shaded [64]


SEASONAL DEVELOPMENT : 
Perennial ryegrass begins growth early in spring.  Peak biomass occurs
during cool moist conditions in spring and again in autumn [18].
Flowering occurs from April or May to August, depending on environmental
conditions [14,46].  Seeds are released in late spring and summer and
germination takes place from August to September or as soon as moisture
conditions allow [18,50].

Anthesis dates from selected western states are as follows [9]:

Colorado      June-August
Wyoming       June-July
Montana       May-July
North Dakota  June-July

In the southern states, perennial ryegrass will remain green through the
winter [14,20].  In a study of climatic variation in the rate of leaf
expansion, Cooper [8] concludes that Mediterranean populations can
expand in leaf area more rapidly in winter than continental populations.
Maritime populations of perennial ryegrass are intermediate.  The
differences appear to be dependent on temperature, perhaps due to past
climatic selection.  Populations in Mediterranean climates are adapted
to mild, moist winters and can grow year-round, but populations in
continental climates are winter dormant.

The peak stem carbohydrate reserve levels occur in early summer, just
after flowering begins, dropping off through summer to a low in October.
This is in contrast to many other grasses that have two peaks of
carbohydrate reserves, one in early spring which is depleted by
flowering, then replenished by late summer.  Apparently, perennial
ryegrass is more efficient at maintaining carbohydrate reserves through
the flowering period [55].

Related categories for Species: Lolium perenne | Perennial Ryegrass