18.
Amaranthus dubius
Martius ex Thellung, Fl. Adv. Montpellier. 38: 203. 1912.
Spleen amaranth
Plants
glabrous or sparsely pubescent in distal parts.
Stems
erect, green, branched, 0.3-1 m.
Leaves:
petiole of proximal leaves equaling or longer than blade, becoming shorter distally; blade rhombic-ovate or ovate to elliptic, 3-12 × 2-8 cm, base broadly cuneate, margins entire, apex slightly acuminate to obtuse and faintly emarginate, mucronate.
Inflorescences
terminal panicles and axillary spikes; panicles erect or often drooping, green, dense, branched, leafless at least distally.
Bracts
lanceolate, shorter than 2 mm, shorter than tepals, apex spinescent.
Pistillate flowers:
tepals 5, oblong-spatulate to oblong, not clawed, 1.5-2 mm, apex acute, often very shortly mucronate; style branches strongly spreading, shorter than body of fruit; stigmas 3.
Staminate flowers
usually clustered at tips of inflorescence branches, sometimes gathered in proximal glomerules (as in
A. spinosus
); tepals 5, equal or subequal; stamens 5.
Utricles
ovoid or subglobose, 1.5-2 mm, slightly shorter than tepals, smooth to irregularly wrinkled, dehiscence regularly circumscissile.
Seeds
dark reddish brown to black, subglobose or lenticular, 0.8-1 mm diam., shiny, smooth.
2
n
= 64.
Flowering summer-fall in tropics, various seasons in subtropics. Waste places, disturbed habitats; 0-100 m; introduced; Fla.; West Indies; South America; introduced and locally naturalized Europe, Asia, Africa.
Amaranthus dubius
, a morphologically deviant allopolyploid, is very close genetically to both
A. spinosus
(sect.
Centrusa
) and members of sect.
Amaranthus
. This species most probably originated as a result of ancient hybridization between
A. spinosus
and either
A. hybridus
or
A. quitensis
(W. F. Grant 1959; T. N. Khoshoo and M. Pal 1972; M. Pal and T. N. Khoshoo 1965; J. D. Sauer 1967b; V. Srivastava et al. 1977).
Amaranthus
nothosect.
Dubia
Mosyakin & K. R. Robertson (
A
. sect.
Amaranthus
×
A
. sect.
Centrusa
), was proposed to accommodate
A. dubius
(S. L. Mosyakin and K. R. Robertson 1996).
