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PROCEEDINGS OF THE CALIFORNIA ACADEMY OF SCIENCES 
Series 4, Volume 65, 28 Sept. 2018, No. 2 
eromorphic, posterior lobe conduplicate or planar, larger or smaller than lateral lobes, subsaccate 
or with a flap at base only in L. parayi, lateral lobes planar. Corolla white, greenish, or yellow (and 
often tinged with maroon), or dark chestnut to maroon, or brownish, relatively large, tube abrupt¬ 
ly expanded into an obliquely bell-shaped and anteriorly saccate throat, narrow proximal portion 
of tube (i.e., from base of corolla to point of insertion of stamens) ± cylindric, limb subbilabiate, 
upper lip 2-lobed, lower lip 3-lobed, lobes subequal, often recurved to recoiled, entire to 2-fid at 
apex, contorted in bud. Stamens 2 (usually accompanied by 2 staminodes near base) or 4 (with 
1 staminode, or staminode either absent or not evident), filaments inserted at or near base of corol¬ 
la throat (i.e., at or several mm distal to apex of narrow proximal portion of corolla tube), usually 
long-exserted from mouth of corolla, glabrous or usually pubescent proximally with eglandular 
trichomes, anthers 2-thecous, thecae elongate, equal in size, parallel to sagittate, equally inserted, 
lacking basal appendages, dehiscing toward lower lip (i.e., flower nototribic), glabrous; pollen 
spheric to subspheroidal, pantoforate with apertures >50, exine gemmate to baculate and with 
additional sparse to dense microsculpturing; staminodes (if present or evident) usually consisting 
of inconspicuous subulate to triangular projections (rarely an elongate sterile filament in section 
Tetrandrium ). Style usually long-exserted from mouth of corolla, stigma 2-lobed and sometimes ± 
funnelform, lobes usually ± flattened, equal to unequal in size. Nectar disk prominent below gynoe- 
cium, up to 3 mm high, annular or ± cupulate. Capsules substipitate to stipitate, relatively large, 
head ovoid to ellipsoid to linear-ellipsoid, septa with attached retinacula remaining attached to 
inner wall of mature capsule. Seeds up to (12) 16 (24) per capsule, disposed in 2 rows in each 
locule, discoid, subcircular to subcordate to subellipsoid in outline, flat surfaces smooth to wrin¬ 
kled and sometimes with papillae or tubercles, lacking trichomes, marginal region ± swollen, 
peripheral edge ± furrowed and densely pubescent with appressed hygroscopic trichomes. 
This genus of 11 species occurs in either seasonally dry or moist to wet regions from north¬ 
eastern Mexico (southern Tamaulipas) to eastern Panama (central Guna Yala). Nine species are 
known from Mexico, with six endemic there. Several of the Mexican species are known from either 
few collections and/or have very restricted distributions within the country. Five species occur in 
Central America with one endemic to Belize, and another restricted to Costa Rica and Panama. 
El Salvador and Nicaragua are the only nations in Central America from which the genus is not 
currently known to occur. 
The three sections of Louteridium treated here correspond to the three clades revealed by 
molecular sequence data (Fig. 1). One of these, section Parcostamium, has not been previously 
recognized, and is based largely on molecular characters. Basic taxonomic information for each 
section and a validating protologue for section Parcostamium are provided below. The three 
sections are also referenced in the key to species. 
1. Louteridium section Louteridium. Type. — Louteridium mexicanum (Baill.) Standi. 
Evergreen shrubs or trees (to 12 m tall); herbaceous stems glabrous or puberulent to pubescent 
with eglandular (and rarely also glandular) trichomes; leaves not seasonally/simultaneously decid¬ 
uous, membranaceous, ± evenly distributed along stems; calyx 17 40 mm long (during anthesis); 
stamens 2. 
The three species of this section ( L . donnell-smithii, L. mexicanum, and L. purpusii ) occur 
from southern Mexico (central Veracruz) into western Honduras (west-central Comayagua). 
2. Louteridium section Parcostamium T.F. Daniel & E. Tripp, sect. nov. Type. — Louteridi¬ 
um costaricense Radik. & Donn. Sm. 
