Abstract
An investigation was made of the taxonomic relationships of
Echinochloa crusea111 and the three closely related species, E. muri—
cata, crus—pavonis and E. paludigena as these taxa occur In the
United States. The investigation involved studies of rx: rphologlcal,
anatomical, cytological and reproductive characteristics. Studies of
gross morphology involving population analysis and herbarium and field
specimens provided the most reliable basis for delimitation of taxa.
Characters found to be of most significance were, anther length,
spikelet size, the shape and character of the tip of lemma of the
fertile floret, spikelet hair length, caryopsis width—length ratio
and embryo—caryopsis length ratio. Other supplementary differentiat—
ing characters selected were, the nature of panicle, the presence or
absence of pustulate based setae on nodes of panicle axis and branches,
awn characters, the presence or absence of a palea in the lower floret,
and the presence or absence of stamens In the lower floret. On the
basis of these characters, seven taxa were recognized fron the
complex, namely, E. muricata var. murlcata, E. muricata var. micro—
stachE, E. paludigena, crus—pavonis, crusgalli var. crusga111,
crusgalli var. frumentacea and E. var.
Microscopic studies of culm and leaf structure of the several
taxa revealed no striking differences between the taxa of the com—
plex. The internal s tructure of the leaf is typically panicoid,
Vith vascular bundles enclosed by a single sheath and chlorenchyma
cells Of the mesophyll somewhat radiating out from the bundle sheath.
Bicellular microhairs in the leaf epidermis were found to be typi.—
cally panicoid and present jn varying frequencies in different taxa.
Microhairs of the membranous palea of the Xos*er floret were found to
be clavate or even somewhat saccate and more of the chloridoid type
than Of the typical panicoid type. Three— or four—celled microhairs
were not infrequent in the palea epideruiis or E. muricata var.
microstachy_a. In the epidermis of most of the taxa studied, papillae
were common on thc long cells. Macrohairs were observed only in
crusgalli var. crusgalli. Prickle hairs were common in some forms
of muricata var. muricata and crusgalli var. zelayensis. The
form Of silica cells varied from saddle shaped, dumbbell shaped to
nodular type.
Cytological studies Of five out of the seven taxa confirmed the
previous report of two levels of ploidy in the complex, the tetra—
= 36, and the hexaploid 2!! = 54.
ploid , 2L
Some positive correlation
was observed between ploidy level and pollen size. Studies of mega—
sporogenesls and embryo sac development showed the development of
characteristic 8—nuc1eate embryo sac and normal sexual reproduction
in five taxa investigated.
The characterization of taxa and determination of their distri—
bution patterns were based in part- on the examination of over 6,000
herbarium specimens . IVO of the four species of the complex have
vide distribution in the United States. One, Echinochloa muricata,
is believed to be a native species in North America and the other,
crusgalli, is generally considered to be adventive. Echinochloa
muricata var. muricata is restricted to the eastern half of the
country. It ranges from New Hampshire and Michigan, south to Okla—
homa and eastern Texas tc Florida. Echinochloa muricata var.
microstachyg has wide distribution throughout the United States but
is most common in the north central, central and south central
States. Echinochloa crusgalli var. crusgalli is present throughout
the United States but is most common in the eastern half of the
country and on the west coast. Echinochloa crusgalli var. frumenta—
cea, recorded mainly from northeastern local Ities, is Only found as
an escape from cultivation. Echinochloa Crusgalii var. zelayensis
mainly Is localized In Texas and adjacent States. Echinochloa crus—
pyvonis has only been reported from California and E. paludigena
is known in the United States only from southern Florida