DANIEL & TRIPP: LOUTERIDIUM : TAXONOMY, BIOLOGY, AND CONSERVATION 69 
Evergreen perennial herbs, shrubs, or small trees (to 3 m tall); herbaceous stems glabrous; 
leaves not seasonally/simultaneously deciduous, subsucculent, ± evenly distributed along stems; 
calyx 23-65 mm long (during anthesis); stamens 2. 
The three species of this section ( L . costaricense, L. parayi, and L. tamaulipense ) together 
span the entire geographic range of the genus, and contain both the northern- and southern-most 
occurring species. These species do not appear to share morphological characteristics that are not 
otherwise found among species in other sections. Section Parcostamium differs from section 
Tetrandrium by having two (vs. four) stamens, leaves that are ± evenly distributed along stems (vs. 
clustered near apex) and are not seasonally/simultaneously deciduous (vs. seasonally deciduous), 
and generally longer calyces (23 to 65 vs. 5 to 32 mm). It differs from section Louteridium by its 
generally smaller habit (perennial herbs, shrubs, or small trees to 3 m tall vs. shrubs to trees to 
12 m tall); leaf texture (subsucculent vs. membranaceous); and generally shorter pedicels (up to 
58 vs. up to 95 mm long). The sectional name is derived from the first three letters of all species 
included in the section. 
3. Louteridium section Tetrandrium A. Richardson. Type. — Louteridium chartaceum 
Leonard. 
Deciduous shrubs or trees (to 12 m tall); herbaceous stems lacking trichomes or pubescent 
with dendritic eglandular trichomes; leaves seasonally/simultaneously deciduous, membranaceous 
to subsucculent, clustered near apex of stems; calyx 5-32 mm long (during anthesis); stamens 4. 
The five species of this section (L. brevicalyx, L. chartaceum, L. dendropilosum, L. koelzii, and 
L. rzedowskianum ) occur from west-central Mexico (Jalisco) to east-central Belize (Belize). 
Key to Species of Louteridium 
la. Stamens 4; leaves ± clustered on stems, seasonally deciduous (i.e., plants leafless for part of the 
year); occurring in dry, deciduous or subdeciduous forests.Sect. Tetrandrium 
2a. Calyx 5-9 mm long, lobes 3.5^1.8 mm long, posterior lobe broadly ovate to subtriangular; 
Guerrero. L. rzedowskianum 
2b. Calyx 10-32 mm long, lobes 7.5-32 mm long, posterior lobe linear to lanceolate to ovate 
to subelliptic to subrhombic-obovate. 
3a. Dendritic trichomes present on vegetative and reproductive structures; inflorescence a 
raceme (i.e., dichasia sessile); Oaxaca. L. dendropilosum 
3b. Dendritic trichomes absent on vegetative and reproductive structures; inflorescence 
usually a thyrse (i.e., dichasia usually pedunculate); western Mexico (Jalisco and 
Michoacan) or Belize. 
4a. Calyx 10-16 mm long, lobes 7.5-12 mm long; corolla externally pubescent with 
glandular and eglandular trichomes; inflorescence rachis pubescence including 
glandular trichomes; capsule 32-42 mm long, pubescent with eglandular and glan¬ 
dular trichomes; style 75-77 mm long; seeds 16-24 per capsule; Michoacan. . . . 
. L. brevicalyx 
4b. Calyx 17-28 mm long, lobes 15-37 mm long; corolla externally glabrous; inflo¬ 
rescence rachis glabrous or pubescent with eglandular trichomes only; capsule 
(20-) 23-30 mm long, glabrous or pubescent with eglandular trichomes only; style 
50-67 mm long; seeds up to 16 per capsule. 
