KEY TO NORTH AMERICAN LYCIUM
A. Endocarp indurate at least in part; fruit 2-few-seeded
B. Fruit not constricted, 2-seeded; leaves linear-terete, ovoid or spatuloid, ovary 1-ovulate in each cell, corolla-loves 4, one half as long to as long as the corolla tube… L. californicum
BB. Fruit constricted, leaves flat, corolla-lobes 5
D. Constriction of the fruit generally near the apex, rarely near the middle, calyx-lobes shorter than the calyx-tube… L. cooperi
DD. Constriction of the fruit near the base or at the middle, leaves glabrous or pubescent
E. Fruit with fertile seeds above and below the constriction; leaves glaucous, glabrous… L. schaffneri
EE. Fruit with fertile seeds above the constriction; lower part fleshy and containing only a few abortive seeds.
F. Calyx-lobes subulate to linear-lanceolate, 1.5-2 times as long as the calyx-tube…L. macrodon
FF. Calyx-lobes oblong-ovate or ovate… L. puberulum
AA. Endocarp not indurate, fruit 2-many-seeded
G. Low shrubs to 60 cm tall, flowers sessile or with pedicels not over 2 mm long, fruit 2-6-seeded; bark light tan or whitish… L. shockleyi
GG. Shrubs taller than 60 cm or, if not that tall, not with above combination of characters
H. Corolla-lobes as long as or longer than the tube… L. carolinianum
HH. Corolla-lobes shorter than the tube
I. Calyx tubular or tubular-campanulate, glandular-pubescent; leaves also glandular-pubescent
J. Stamens exserted, flowers pendant… L. exsertum
JJ. Stamens not exserted, flowers not pendant… L. fremontii
II. Calyx cup-shaped, campanulate or tubular, but if tubular not glandular-pubescent
K. Calyx-lobes about as long as or longer than the calyx-tube
L. Leaves glabrous, glaucous... L. pallidum
LL. leaves pubescent
M. Corolla-tube broadly campanulate; calyx-lobes unequal, broadly ovate, acute, some lobes often obsolete, more or less keeled… L. brevipes
MM. Corolla-tube narrowly funnel-form; calyx-lobes subequal, broadly ovate, acute to obtuse, not keeled… L. parishii
KK. Calyx-lobes shorter than the tube
N. Calyx glabrous, 3-lobed, 3-keeled, the lobes white-ciliate-lanate… L.leiospermum
NN. Calyx not as above
O. Corolla-lobes densely ciliate-lanate… L. torreyi
OO. Corolla-lobes either smooth or ciliate, but not ciliate-lanate
P. Filaments sparsely pilose to glabrous at their free base
Q. Corolla tubular to narrowly funnel form, very gradually widening upward, not more than 2 mm wide at the throat, the lobes not more than one-third the length of the tube; leaves glabrous or with hairs not perpendicular to the epidermis… L. andersonii
QQ. Corolla obconic-funnel form, lobes shorter or longer than one third the length of the tube; leaves glabrous or with hairs perpendicular to the epidermis.
R. Stamens not exserted or only slightly so; branches thick, knotty… L.densifolium
RR. Stamens exserted; branches not knotty
S. Calyx and leaves pubescent… L.texanum
SS. Calyx and leaves glabrous… L.arochae
PP. Filaments densely pubescent at base of free portion
T. Leaves pubescent… L. brevipes
TT. Leaves glabrous or very sparsely pubescent
U. Pedicels 8-20 mm long, corolla-lobes more than two-thirds the length of the tube… L. nodosum var. isthmense
UU. Pedicels not more than 9 mm long, corolla-lobes not more than half the length of the tube
V. Calyx tubular-campanulate, 3.5-5 mm long, corolla tubular-infundibuliform…L. megacarpum
V. Calyx cup-shaped, less than 3 mm long, corolla obconic-infundibuliform…L. berlandieri