indigo bush (Amorpha fruticosa)
desert false indigo
tall indigo bush
Amorpha angustifolia (Pursh) Boynt.
Amorpha bushii Rydb.
Amorpha croceolanata P.W. Watson
Amorpha curtissii Rydb.
Amorpha dewinkeleri Small
Amorpha fruticosa L. var. angustifolia Pursh
Amorpha fruticosa L. var. croceolanata (P.W. Watson) P.W. Watson ex
Amorpha fruticosa L. var. emarginata Pursh
Amorpha fruticosa L. var. oblongifolia Palmer
Amorpha fruticosa L. var. occidentalis (Abrams) Kearney & Peebles
Amorpha fruticosa L. var. tennesseensis (Shuttlw. ex Kunze) Palmer
Amorpha occidentalis Abrams
Amorpha occidentalis Abrams var. arizonica (Rydb.) Palmer
Amorpha occidentalis Abrams var. emarginata (Pursh) Palmer
Amorpha tennesseensis Shuttlw. ex Kunze
Amorpha virgata Small
CONFIRMATION STATUS: Confirmed.
TAXONOMY: The currently accepted scientific name of indigo bush
is Amorpha fruticosa L.
NATIVE STATUS: Native, United States and Canada.
GENERAL BOTANICAL CHARACTERISTICS: This is a native
shrub about 4-16' tall that branches occasionally. The lower stems are
woody; the gray bark is relatively smooth with scattered small lenticels.
The upper stems are dull light green and pubescent. The alternate leaves
are about ½–1½' long and odd-pinnate with 11-35 leaflets; they have
relatively short petioles up to 2" long. Both the petioles and central stalks
of the leaves are light gray-green and pubescent. Individual leaflets are
1-2" long and ½–1" across; they are dull gray-green, oblong to broadly
oblong, smooth along their margins, and sparsely canescent-pubescent.
From the leaflet undersides, scattered translucent glands are visible that
resemble small dots. Each leaflet has a tiny pointed tip. The petiolules of
the leaflets are slender and short. Occasionally, clusters of 1-6 spike-like
racemes of flowers develop from the upper branches. Individual racemes
are erect to ascending, 3-8" long, and cylindrical in shape from the dense
arrangement of flowers. Each flower is ¼" long (or a little more) and tubular
in shape from a single violet-purple petal (the standard) that wraps around
the reproductive organs; there is a single style and about 10 stamens that
are strongly exerted. The anthers of the stamens are bright orange-yellow.
The flowers are replaced by small seedpods about ¼" long (or a little more)
that each contain 1-2 seeds. The seedpods are obovoid and somewhat flat-
tened, terminating in short beaks; their outer surfaces are glandular-punc-
tate. The root system is woody and branching. Sometimes small colonies of
plants develop at favorable sites.
REGENERATION PROCESS: Indigo bush propogates itself by reseeding.
SITE CHARACTERISTICS: Indigo bush prefers full or partial sun
and wet to moist conditions. False indigo adapts to different kinds of soil,
tolerating occasional flooding. With the assistance of symbiotic bacteria,
it fixes nitrogen in the ground.
SUCCESSIONAL STATUS: Insufficient information concerning the suc-
cessional status of indigo bush. Indigo bush is usually found in riparian or
lakeshore environments, and it is sometimes found in moist upland loca-
tions; however, it is not common in mature, non-mesic situations.
SEASONAL DEVELOPMENT: The blooming period occurs from late
spring to early summer and lasts about 2-3 weeks.
GENERAL DISTRIBUTION: Indigo bush is found throughout the
United States (except Montana and Nevada) and most of Canada east
of Manitoba (excepting the maritime provinces).
SKY MEADOWS DISTRIBUTION:
Shrub specimens can be found on trails marked in red.
Appalachian Trail/Old Trail
South Ridge/North Ridge
Rolling Meadows/ Lost Mountain
HABITAT TYPES AND PLANT COMMUNITIES: Habitats include
riverbanks, soggy thickets, open bottomland woodlands, edges of marsh-
land, and wet prairies along rivers. It is likely that populations of this
shrub have been declining because of habitat destruction.
IMPORTANCE AND USES: The flowers are pollinated primarily by
small to medium-sized bees, which seek nectar and pollen. These bee
visitors include Halictid bees (Lasioglossum spp.), Masked bees (Hylaeus
spp.), Andrenid bees (Andrena spp.), Little Carpenter bees (Ceratina spp.),
and Cuckoo bees (Nomada spp., Coelioxys spp.). The Andrenid bee,
Andrena quintilis, is a specialist pollinator (oligolege) of Amorpha spp.,
including false indigo. The caterpillars of Epargyreus clarus (silver-
spotted skipper), the butterfly Colias cesonia (dogface sulfur), and the
moth Dasylophia anguina (black-spotted prominent) feed on foliage of
false indigo, while the caterpillars of the moth Pleuroprucha insularia
(common tan wave) feed on the flowers. Other insects that feed on this
shrub include the lace bug Gargaphia amorphae, the plant bugs Psallus
amorphae and Lopidea hesperus, and the larvae of the long-horned
beetle Megacyllene decora (which bore through the stems). There are
also several leaf beetles that feed on the leaves (Anomoea flavokansiensis,
Anomoea laticlavia, Odontata dorsalis, Phyllecthris dorsalis, and
Sumitrosis rosea). White-tailed deer browse on this shrub sparingly.
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