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PROCEEDINGS OF THE CALIFORNIA ACADEMY OF SCIENCES 
Series 4, Volume 65, 28 Sept. 2018, No. 2 
mann 11913 reveal that no flowers were open between 16:00-17:30 on the first day of observa¬ 
tions, but several very large floral buds were present. On the following day, all of the large buds 
were found to be fully open at 08:30, and no visitors were noted over the course of an hour. 
Distribution and habitat. — West-central Mexico (Michoacan; Fig. 8); plants occur on 
exposed limestone, often on steep slopes of arroyos, in tropical subdeciduous forests at elevations 
from 200 to 590 meters. 
Illustrations. — Figure 2A-E; Richardson (1972:66, fig. 2). 
Conservation. — Except for L. rzedowskianum, which is known from a single site, L. brevi- 
calyx has the smallest known EOO (0.27 km 2 ) among its congeners. At the site of Daniel & Stein- 
mann 11913, about 100 plants were seen growing, mostly epipetrically, in an area of ca. 5000 m 2 
on exposed limestone slopes in forest. No protected land appears to be within the species EOO. 
Evident threats to this species appear to be large-scale mining in the vicinity of Daniel & Stein- 
mann 11913 (ca. 1.5 km distant) and deforestation for agriculture (including cattle) that is evident 
within the small EOO and in adjacent regions. Given the size of the EOO and apparent major threat 
(i.e., deforestation for agriculture), a single location is evident. A preliminary conservation assess¬ 
ment of Critically Endangered (CR; Bl, a, b; IUCN 2017) is proposed for L. brevicalyx. 
Discussion. — Leaves are absent on the field specimens examined. Information on young 
stems and leaves provided above is from cultivated plants ( Daniel & Steinmann 11913cv). Leaves 
of these plants may not have attained the maximum size encountered in natural settings. The inflo¬ 
rescence, which appears before the leaves, arises from the apex of the previous season’s woody 
growth and bears a stalked (pedunculate) thyrse or a sessile rachis subtended by axillary dichasia 
(sessile thyrse). A stem forms with the flush of new clustered leaves later in the season. 
Most calyces have the three lobes that are characteristic of the genus. Five lobes with three 
prominent lobes and two reduced lobes are evident on Hinton et al. 15843; the reduced lobes are 
3 to 6 mm long and 0.8 to 2 mm wide. Five-lobed calyces in inflorescences are likely teratological 
and suggest suppression rather than fusion of lobes for typical plants with three-lobed calyces. 
Additional specimens examined. — MEXICO. Michoacan: Mpio. Aquila, KM 6.7 car- 
retera Aquila-Coalcoman, 18°36’38”N, 103°28’32”W, P. Carillo-Reyes & V Steinmann 5484 
(CAS, RSA); between Coalcoman and Aquila, 5.6 km NE of Aquila, 18°36’32.54”N, 
103°28’31.38”W, T. Daniel & V. Steinmann 11913 (CAS, COLO, MEXU, MO, NY, US), cultivat¬ 
ed plants of this collection grown from seed in San Francisco, California, 11913cv (CAS); Aquila 
[ca. 18°35’49.39”N, 103°30’14.64”W], G. Hinton et al. 15843 (RSA, US). 
2. Louteridium chartaceum Leonard, Publ. Carnegie Inst. Wash. 461:197. 1936. Type.— 
BELIZE. Belize: Gracie Rock, Sibun River [ca. 17°23’13.67”N, 088°27’1.91”W], 24-III-1935 (fir, 
frt), P. Gentle 1526 (holotype: US-1589669!; isotypes: A-image seen, ARIZ!, K!, LL!, MICH!, 
MO!, NY!, US-1589668!, WIS-image seen). 
Shrubs to trees to 3.5 m tall, often epipetric. Older (woody) stems irregularly striate, ± lenti- 
cellate, lacking trichomes; younger (herbaceous) stems subterete to subquadrate, glabrous. Leaves 
seasonally deciduous, ± clustered just proximal to inflorescence, petiolate (or distal leaves subses- 
sile), petioles to 70 mm long, blades subsucculent, ovate to elliptic (to obovate-elliptic), 70-285 
mm long, 30-95 mm wide, 1.7-3.7 x longer than wide, acuminate to subfalcate at apex, rounded 
Figure 12 (right). Louteridium chartaceum {Brewer 7176). A. Flower. B. Habit of young plant showing clusters of 
leaves. C. Trunk of mature plant growing on rocky slope. D. Portion of mature leaf showing red to pink veins and margin¬ 
al swellings/encrustations. E. Older stem showing swelling above nodes, raised lenticels, and leaf scars. F. Inflorescence 
with lateral short shoots, persistent calyces on old flowers, and a nearly mature floral bud. Photos by S. Brewer (to whom 
copyrights are reserved), used with permission. 
