BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Melilotus alba | White Sweetclover 



GENERAL BOTANICAL CHARACTERISTICS : 
Annual forms of white sweetclover exist, but the plant is primarily
biennial.  First-year plants are comprised entirely of vegetative growth
(usually a single stem) and overwinter as buds on the caudex.
Second-year plants have a strongly developed taproot which may exceed 50
inches (120 cm) in depth, and 1 to 10 upright or ascending flowering
stems from 3 to 8.5 feet in height [31,33].  The inflorescence is a
raceme with 40 to 80 white flowers.  The fruit is a one-seeded pod.


RAUNKIAER LIFE FORM : 
   Hemicryptophyte (biennial form)
   Therophyte (annual form)


REGENERATION PROCESSES : 
White sweetclover is a good seed producer.  Seed production estimates of
14,000 to 350,000 seeds per plant have been reported.  Large plants
growing in the open in Ontario produced between 200,000 and 350,000
seeds each.  The fruits are shed in the fall, and are dispersed by
gravity, strong winds, and water.  The seeds float, and thus rain wash
and stream flow may be an important means of dispersal [34].  A large
percentage of the seeds have a hard seed coat and can remain viable in
the soil for more than 20 years [31].  Natural scarification occurs
through fluctuating freezing and thawing temperatures or by heat from a
fire [15].  New seedlings are found almost any month during the growing
season, but only spring-emerged seedlings survive the winter [17,34].

Vegetative reproduction:  Vegetative reproduction does not occur
naturally.  If second-year plants are cut, new growth must come from
buds on the stems rather than the caudex [31].


SITE CHARACTERISTICS : 
White sweetclover is shade intolerant and grows in a wide variety of
open habitats but is most common along roads and railways, and in
prairies, arid rangelands, fields, and waste places [16,34].  Its
associates are too numerous to list, but it often grows with yellow
sweetclover (Melilotus officinalis) in the West [1].  It is not tolerant
of continuous flooding but occasionally grows on open, gravelly
riverbanks that experience brief spring flooding.  White sweetclover
grows on a wide range of soil types and textures from clay to dune sand
and river gravels [34].  It is most commonly found on calcareous soils.
It grows poorly on acid soils [31,34].  It requires sufficient moisture
for establishment but is thereafter very drought tolerant [34].


SUCCESSIONAL STATUS : 
Obligate Initial Community Species

White sweetclover is an early colonizer of disturbed sites.  It is
common on strip-mined lands in the central and eastern United States
[9,16].  Turkington [34] reported that it may be eliminated from an area
within 2 years if the ground surface is covered by perennial species
because seedlings cannot survive in a perennial sward.  Other
researchers have detailed its persistence in many native and established
tallgrass prairies; however, its abundance in these communities was
probably due to periodic disturbance (fire) [15,18].  It was found in
oldfields in Ohio but disappeared from sites when tree cover became
continuous [26].


SEASONAL DEVELOPMENT : 
First-year plants:  Nearly all energy in the early part of the growing
season is put into top-growth.  In late summer, however, the tops grow
very little, while the roots grow dramatically.  This is the "critical
growth period" when plants allocate most energy to root growth.  Root
weight of first-year plants grown near Ames, Iowa, was as follows [21]:

     Date      Root Weight (grams)

     June 4           24.5
     July 3          118
     August 4        430
     September 3     448
     October 3      1609
     November 6     2388

Second-year flowering shoots become noticeable as root crown buds about
the time rapid root growth begins.  First-year shoots are killed by
freezing temperatures in the fall or winter.

Second-year plants:  In the spring of the second year, several shoots
arise from the root crown and elongate rapidly.  By midsummer, each
shoot bears many flowers, and flowering may continue until early fall.
Flowering for several locations has been reported as follows [6,41].

       Location          Flowering time

     Colorado            June through September
     Montana             July through August 
     North Dakota        June through September
     Utah                May through July
     Wyoming             June through September
     New England         June 9 to September 25  

Blooming usually occurs earlier during hot, dry years [40].

Related categories for Species: Melilotus alba | White Sweetclover