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