BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Melilotus officinalis | Yellow Sweetclover 



GENERAL BOTANICAL CHARACTERISTICS : 
Yellow sweetclover is 20 to 60 inches (50-150 cm) tall.  It is a
biennial legume, with a narrow root crown producing 1 to 10 upright
stems; short, erect rhizomes; a deep taproot; and adventitious roots
that extend the root diameter to 12 to 16 inches (30-40 cm) [62,64,67].
The roots form nodules when infected with Rhizobium bacteria, but no
mycorrhizal associates have been reported [67].
 
Yellow sweetclover will take up molybdenum at a higher rate than
grasses, maintaining a low copper to molybdenum ratio when grown on
sites with high concentrations of those metals [14].


RAUNKIAER LIFE FORM : 
   Therophyte
   Hemicryptophyte


REGENERATION PROCESSES : 
Yellow sweetclover reproduces by seed.  The seeds are "hard" (impervious
to water) and require scarification before germinating.  Natural
scarification occurs through freezing and thawing; passage through
animal digestive tract; or by fire.  The seeds remain viable for 40 or
more years, and can be either wind dispersed, carried by rainwater, or
carried by animals [62,64,67].  Yellow sweetclover is winter hardy, with
contractile roots that pull the crown 2 inches (5 cm) or more below the
soil surface in the fall.  No vegetative reproduction appears to occur
in this species [64,67].


SITE CHARACTERISTICS : 
Yellow sweetclover will grow on a wide variety of soil types and is
tolerant of saline and alkaline soils [21,63,69].  It is not tolerant
of acidic soils [33,63].  Often found on disturbed sites, yellow
sweetclover can occupy a wide variety of sites, including roadsides,
railroad beds, sand bars, and prairie dog colonies [46,52].  It is
highly drought tolerant; water stress is critical only for a short
period during germination [55,69].

Some common associates of sweetclover include white sweetclover
(Melilotus alba), quackgrass (Agropyron repens), wild carrot (Daucus
carota), black medic (Medicago lupulina), buckhorn plantain (Plantago
lanceolata), goldenrod (Solidago spp.), common dandelion (Taraxacum
officinale), milkweed (Asclepias syriaca), timothy, red clover
(Trifolium pratense), and white clover (T. repens) [66].

Associates of yellow sweetclover in riparian zones dominated by Kentucky
bluegrass (Poa pratense) are slender wheatgrass (Elymus trachycaulus
ssp. trachycaulus), sedge (Carex spp.), mannagrass (Glyceria spp),
Baltic rush (Juncus balticus), field horsetail (Equisetum arvense),
common yarrow (Achillea millefolium), Aster spp., clover (Trifolium
spp.), and lupine (Lupinus spp.) [11].


SUCCESSIONAL STATUS : 
Obligate Initial Community species

Yellow sweetclover is not tolerant of shade.  In a study of secondary
succession in New Jersey, it was found only on newly abandoned fields (2
years) and not on older sites [4,67].  In a study of succession,
Eichhorn [21] found it in various cover percentages (not steadily
increasing or decreasing) up to 18 years following a wildfire in
Montana.  Rietveld [56] found yellow sweetclover as an invader species
in a ponderosa pine/bunchgrass community, able to colonize disturbed
areas.  If the ground surface is covered by perennial species, yellow
sweetclover tends to be eliminated, although it will persist on sites
that have periodic disturbances [30,67]

Roberts [57], in a seed bank study of secondary succession, found
sweetclover seeds only on early seral sites.


SEASONAL DEVELOPMENT : 
Germination of yellow sweetclover can occur at any time of year, with
the largest flush of new seedlings in March and April.  The first year
of growth involves a primary, branched stem and a primary root,
sometimes branched.  Yellow sweetclover only rarely flowers the first
year.  The first year is characterized by rapid top growth through late
summer, then a critical growth phase that occurs in mid-September, in
which carbohydrates and nitrogen are transferred to the roots.  During
this phase and into winter dormancy the crown buds become enlarged and
conspicuous.  First year shoots die back with freezing temperatures
[67].

The second year of growth begins in early spring with rapid growth from
the crown buds or rhizomes, using the previous fall-accumulated
reserves, which are not replenished.  Flowering begins in May and June,
continuing through frost, with seed set in June and July [62,67].

Related categories for Species: Melilotus officinalis | Yellow Sweetclover