Important!
Please read before using subkey
Common names mesquite
Description
Fruit with two longitudinal sutures; straight, curved,
twisted, or loosely to tightly spirally coiled; compressed to terete,
with straight or undulate to moniliform margins. 6-35 seeds per pod. Exocarp
thin, leathery to woody, variously colored. Mesocarp fleshy, sugary or
fibrous. Endocarp divided into one-seeded, bony, fibrous or coriaceous
segments; endocarp segments closed, or open and continuous in between
and partially surrounding each seed; seeds oriented longitudinally or
rarely biseriate and transverse.
Seeds mostly obovate, also round, elliptic, oblong
or rhombic, partly compressed to compressed, hard, light straw-yellow
to reddish brown, dark brown or greenish, semiglossy to glossy, smooth,
both faces with a pleurogram, and with or without an umbo. Hilum punctiform,
basal to subbasal, often obscured by filiform funiculus remnant to 7 mm
long. Lens generally discernible, just apical to hilum, +/- round, mounded
to recessed, often whitish in color, up to 0.5 mm long. Embryo investing,
cotyledons expanded, flat and thick, the lobes concealing margins of radicle,
or concealing all but tip of radicle; cotyledons ca. as long as to three
times as long as the hypocotyl-root axis; embryonic axis straight to slightly
deflexed; endosperm mucilaginous.
More about fruits
In Prosopis, the fruit is technically not
a legume, as it does not dehisce along its sutures. Pods of some species
are eaten, while some may disintegrate, releasing endocarp segments that
contain seeds. Other species' pods split transversely into one-seeded
pod segments. Prosopis pods have been variously called 'legume',
'drupaceous loment', 'lomentum', or 'camara' by different authors.
Seeds are oriented within the pods either longitudinally,
in which the seeds lie flat (like the pod itself) and more or less oblique,
or transversely, in which the seeds lie on their edges, perpendicular
to the pod axis. (Figure 1).
More about seeds
The pleurogram is a U-shaped line on both seed faces,
resulting from modification of the face of the ovule during seed development.
It is usually visible, though it may be faint. Within the Fabaceae, pleurograms
are found in the seeds of some genera in Mimosoideae and occasionally
in genera of Caesalpinioideae. The area within the pleurogram is typically
about one third the width of the seed. Pleurograms may be broadly open
to nearly closed, with arms straight to rounded, and with the ends of
the arms typically situated two-thirds to three-quarters of the way down
the length of the seed.
The umbo is a rounded protuberance on both faces of
some Mimosoid seeds.
The lens (Figure 2) is a mound, pad, or area of tissue
situated near the hilum on seeds in the Mimosoideae and Caesalpinioideae.
The lens is discernible in about 50% of Mimosoideae genera. In Prosopis,
the lens is usually roundish, whitish or yellowish, and raised, flush,
or recessed. Because in Prosopis the hilum is punctiform and
rather inconspicuous, the lens can be easily mistaken for the hilum. If
a funiculus remnant adheres to the hilum, the distinction between the
two is clear.
Identification remarks
The pods of some Prosopis species can be
distinguished from those of other genera because they are indehiscent,
and separate or disintegrate into hard, one-seeded, non-winged fruit segments
composed of the endocarp layer. (The pods of other Prosopis species
(e.g. P. farcta and P. ferox), however, do
not break into endocarp segments although the endocarp is segmented.)
Additionally, within Prosopis, many of the pods can be distinguished
based on certain features. Prosopis seeds, however, look very
similar; determination to species may be difficult at best. Furthermore,
Prosopis seeds may look similar to those in other Mimosoideae
genera.
What is the disseminule?
In Prosopis, depending on the species, pods, one-seeded pod
segments, one-seeded endocarp segments, or seeds may all be considered
disseminules. Prosopis pods are indehiscent, so the seeds are
not released directly. In some species, the fruit mesocarp is fleshy and
is eaten by animals. The seeds pass through the animals' digestive tracts
unharmed and can then germinate. In other species, the mesocarp is fibrous
or bitter. The exocarp and mesocarp of these pods may deteriorate in or
on the soil upon exposure to the elements, releasing endocarp segments
or seeds. Eventually, the endocarp segments may degrade or split open,
exposing or releasing the seeds.
Distribution
Southwest Asia, Africa; predominantly America, from
western North America to Patagonia.
Only four species are native to Southwest Asia and Africa. The remaining
species in the genus are native to Mexico and South America, with the
center of polymorphism in Argentina.
General information
The genus Prosopis comprises almost 50 species, 25 of which
are on the the list of federal noxious weeds. Prosopis are most
often spiny trees or shrubs predominantly well adapted to hot, arid climates.
Some Prosopis species have invasive, weedy tendencies, forming
thickets of spiny shrubs that prevent the use of pastureland. On the other
hand, many Prosopis species are considered valuable in their
native range. The wood is valued for timber and fuel. The plants have
also been used for cordage, dye, gum, and medicine. Prosopis trees
are an important part of the vegetation in arid climates, providing shade,
firewood and forage, and have been used in reforestation efforts in these
climates. Additionally, some consider Prosopis spp. valuable
for the development of food crops. The pods of some species are fleshy
and eaten by livestock, and some can be ground into flour.
IMPORTANT INFORMATION!
PLEASE READ BEFORE USING SUBKEY:
Seeds
Seeds of Prosopis species are not found in abundance. One reason
for this is that the pods are indehiscent and hold the seeds tightly.
As a result, for most of the Prosopis species in this subkey,
both the descriptions and images of seeds in the fact sheets, and the
morphological scoring data underlying the subkey are based on the examination
of very few seeds. Therefore, use of the subkey and fact sheets may not
necessarily lead you to the correct species. Please note the following:
The seeds of different Mimosoideae species often look
very similar.
Within-species morphological variability of seeds may
not be represented in the fact sheets or subkey.
Although pleurogram appearance may vary within a species,
in this key the pleurogram character has been constructed so that it hopefully
detects extremes of pleurogram morphology that may be species-specific.
Mimosoideae seeds darken with age; color is not a good
character for identification.
Pods
Prosopis pods change color and appearance as
they ripen and age. The pod images in this key may represent only one
developmental stage, although most of the images are of more or less mature
pods.
The images of Prosopis pods in this key may not
represent within-species morphological variability.
Morphological features of pods are usually characteristic
of individual species. Some reliable features are pod proportions, number
of coils, and degree of flattening.
Recommendations
Use the subkey fruit characters and images if a pod
is available.
If your seed or pod is noticeably distinctive looking
(you'll get an idea for what that is by looking at images of all the species),
there is a higher likelihood you will be able to identify it to species.
If your identification is uncertain, seek the advice
of an expert.
Subkey
to Prosopis species |
Prosopis glandulosa
Photo: © J.R. Manhart
Prosopis sp. Pods
Photo © D. Bailey
Figure 1. Seed orientation; pods shown
in longitudinal section. Lines surrounding seeds indicate endocarp segments
or chambers
Figure 2. Hilar area of seed (in marginal
view) |
