Louteridium dendropilosum T.F. Daniel, 2017

Daniel, Thomas F., 2017, New and Reconsidered Mexican Acanthaceae XII, Proceedings of the California Academy of Sciences 64 (7), pp. 131-154 : 140-144

Louteridium dendropilosum T.F. Daniel , sp. nov.

Louteridium dendropilosum differs from its congeners by the following combination of characters: epipetric habit, four stamens, and dendritic trichomes on some vegetative and reproductive organs.

TYPE.— MEXICO. Oaxaca: Distr. Pochutla, Mpio. San Miguel del Puerto, Arroyo Arena , ca. 100 m downstream from jct. Río Laja , ca. 3 km SE of Rancho Dioon toward Xadani , 15°58’51.33”N, 096°05’53.91”W, 600 m, evergreen seasonal forest (selva mediana subperennifolia), 29-III-2011 (flr, frt), T . Daniel , A . Sánchez , & J . Pascual 11784 (holotype: MEXU!; isotypes: CAS!, COLO!, K!, MO!, NY!, SERO!, US!).

Shrubs to trees to 12 m tall, frequently epipetric, larger individuals with prop trunks/roots. Older (woody) stems quadrate, lenticellate, irregularly striate-sulcate, lacking trichomes; younger (herbaceous) stems subquadrate-sulcate [terete on fresh stems], sparsely lenticellate, irregularly fissured, [lacking trichomes on fresh stems] evenly pubescent with erect to flexuose simple and dendritic (sparse) eglandular trichomes <0.1– 0.5 mm long. Leaves deciduous, often ± clustered at apex of old growth or at apex of an otherwise leafless shoot of new growth, petiolate, petioles often tinged with pink or red, to 60 mm long, blades subsucculent, ovate to elliptic to broadly elliptic, 76–180 mm long, 40–107 mm wide, 1.4–2.5 × longer than wide, apiculate to acuminate at apex, rounded to acute to attenuate at base, adaxial surface pubescent with simple and dendritic eglandular trichomes, trichomes soon becoming ± restricted to proximal portion or to midvein, abaxial surface pubescent (especially along veins) with dendritic trichomes to 0.5 mm long, midvein often pinkish or reddish, margin entire (sometimes undulate and appearing subcrenate). Inflorescence a terminal subsessile to pedunculate dichasiate raceme to 220 mm long, peduncle to 50 mm long, pubescent like young stems, rachis pubescent like young stems; dichasia opposite or alternate, sessile, 1-flowered, to 47 mm long. Bracts caducous, not seen. Bracteoles caducous, not seen. Flowers pedicellate, pedicels 21–46 mm long, pubescent like rachis or with the trichomes to 1 mm long. Calyx 17–32 mm long, lobes subhomomorphic to subheteromorphic, membranaceous, subelliptic to ovate-elliptic to subrhombic-obovate, rounded to acute at apex, abaxially pubescent with mostly dendritic trichomes 0.1– 0.5 mm long, posterior lobe planar, 17–32 mm long, 10–19 mm wide, usually slightly larger and sometimes more conspicuously venose than lateral lobes, major veins often maroon, lateral lobes planar, 20–31 mm long, 8–18 mm wide. Corolla light green or greenish yellow, sometimes with maroon on limb (especially at base of lobes) and distal portion of throat, externally glabrous (inconspicuously glandular punctate but lacking elongate trichomes), 50–62 mm long, tube 35–37 mm long, narrow proximal portion of tube 11–15 mm long, 6–10. 5 mm diameter near midpoint, throat 20–24 mm long, 25–35 mm diameter at mouth, lobes recurved to recoiled, broadly ovate-subtriangular, 13–20 mm long, 10–21 mm wide, entire at apex. Stamens 4, 60–80 mm long, filaments glabrous distally, pubescent with eglandular trichomes near base (i.e., fused portion of pairs), pairs fused at base up to 9 mm, thecae 8–10. 5 mm long; staminode consisting of a rodlike projection 0.6 mm long in dorsalmost position; pollen subspheroidal to spherical ( P: E = 0.96–1.04), pantoporate, 114–131 µm in diameter, exine surface microrugulate to microverrucate and with overstory of gemmae and/or bacculae. Style 70–101 mm long, distally glabrous, pubescent with eglandular and glandular trichomes near base, stigma equally 2-lobed, lobes flattened, broadly elliptic, 1–2 mm long, 1– 1.4 mm wide. Capsule 25–28 mm long, densely pubescent with erect glandular trichomes 0.05– 0.5 mm long and with an overstory (sometimes sparse) of erect to flexuose (sometimes dendritic) eglandular trichomes to 1.4 mm long, stipe 2.5– 3.5 mm long. Seeds to 16 per capsule, 5. 2–7 mm long, 5–6. 4 mm wide, surfaces smooth and lacking trichomes, margin ± thickened, densely pubescent with hygroscopic trichomes expanding to 0.5 mm long when moistened (appearing as a ± solid to irregularly eroded peripheral band when dry). PHENOLOGY.— Flowering: February–March; fruiting: March–April. As in some other species of Louteridium , flowering takes place during the dry season when leaves are often absent (e.g., February). Near the end of the dry season (e.g., late March) when flowering is waning and fruits are mature, a new flush of vegetative growth appears from axils of clustered leaf scars at the base of the inflorescence (which eventually falls away). As the cluster of new leaves develops (fig. 7), internodal stem growth takes place between at least one of the pairs and the remaining cluster (e.g., the young stems of the description above). DISTRIBUTION AND HABITAT.— Southern Mexico (central southern and southeastern Oaxaca; Fig. 6); plants occur on karstic slopes of streams in evergreen seasonal forest (selva mediana subperennifolia) and tropical deciduous forest (bosque tropical caducifolio) with Beaucarnea , Brosimum , Bursera ,

FIGURE 6. Map of southern Mexico with distributions of Louteridium Lonchocarpus ) at elevations dendropilosum (Oaxaca) and L. rzedowskianum (Guerrero). from 600 to 750 m.

ILLUSTRATIONS.— Figures 7 , 8.

CONSERVATION.— This species is known only from the Sierra Madre del Sur and the Isthmus of Tehuantepec in Oaxaca, consisting of two locations ca. 137 km apart. The EOO is 32.1 sq. km. None of known occurrences is on protected lands. At the type locality in 2014, about 50 mature plants were observed in an area of ca. 2250 square meters on rocky limestone slopes above a stream. Much or all of this locality has since been destroyed by road-building activities at that site ( S. Salas, pers. comm. in March 2015). With on-going development of these and other types (e.g., agricultural) of human disturbances at one of the two locations, a decline in populations or population sizes has been observed and would seem likely to continue. Thus , a preliminary assessment of Endangered (En) is proposed for this species ( B1 , a, b; IUCN 2017). PARATYPES.— MEXICO. Oaxaca: Distr. Pochutla , Mpio. San Miguel del Puerto , Arroyo Arena , ca. 100 m downstream from jct. Río Laja, ca. 3 km SE of Rancho Dioon toward Xadani, T . Daniel, E . Lott, J . Pascual, and N . Salas M . 11894 ( CAS, MEXU); Mpio. El Barrio , 9 km N [sic] de El Barrio, Cerro Palmasola, antena microondas [ca. 16°44’32.52”N, 095°05’36.04”W], R . Fernández N . 4189 ( IEB, NY); Distr. Pochutla , Mpio. San Miguel del Puerto, Arroyo Arena, 15°58’39.7”N, 096°05’54.9”W, J . Pascual 1396 ( MEXU, SERO, TEX); Distr. Pochutla , Mpio. San Miguel del Puerto, 300 m de la terracería sobre la vereda rumbo Río la Laja, 15°58’49.9”N, 096°06’6.9”W, A . Saynes V . et al. 3831 ( MEXU, SERO); Distr. Juchitán , Mpio. El Barrio, parte alta del Cerro Palmasola, junto a la antena de microondas [ca. 16°44’32.52”N, 095°5’36.04”W], S . Zamudio R . 6352 ( CAS, IEB).

DISCUSSION.— Pollen of Louteridium dendropilosum ( Fig. 4F, I ) resembles that of its congeners. The posterior calyx lobe of this species is conspicuously venose with the major veins purple, whereas the lateral lobes are green ( Fig. 7 ). A major morphological distinction among species of Louteridium S. Wats. is the number of stamens (two vs. four). This distinction does not appear to correlate with either geography or molecular phylogenetic relationships (based on the limited sampling to date; Tripp et al. 2013). Louteridium dendropilosum is unique among congeners by its dendritic trichomes, which are present on both vegetative and reproductive organs. Trichomes of other species may consist of one or more cells and be either glandular or eglandular, but they are not branched.

Figures

FIGURE 7. Louteridium dendropilosum. From left to right and top to bottom: habit of two 4-year old plants germinat- ed from seeds; trunks and prop roots of epipetric plant; flower with dorsal calyx lobe, yellowish green corolla, androecium (with two stamens partially broken off), and style+stigma; inflorescence with two flowers having just opened at night; nearly mature flower bud with dorsal calyx and one lateral calyx; recently opened flower showing four fertile stamens and style/stigma; greenish purple corolla with stamens in side view and front-view. Three photos on left from Daniel et al. 11784; all others from Daniel et al. 11894.

FIGURE 8. Louteridium dendropilosum (Daniel et al. 11784). A. Habit with new growth. B. Mature leaf. C. Trichomes from abaxial leaf surface. D. Inflorescence in fruit from woody shoot. E. Flower. F. Calyx lobes (dorsal on left, one of laterals on right). G. Stigma. H. Dehisced capsule. I. Capsule (internal view). J. Seed. Drawn by Noel Pugh.

FIGURE 4. Pollen of Acanthaceae. A, B. Carlowrightia yucatanensis (Daniel et al. 10320), apertural view (A) and interapertural view (B). C. Justicia zapoteca (Saynes V. & Elorsa 2741), apertural view. D, E. Poikilacanthus foliosepalus (Hernández O. 326), apertural view (D) and interapertural view (E). F. Louteridium dendropilosum (Fernández N. 4189). G, H. Poikilacanthus pochutlensis (Torres & Martínez 4907), subpolar view (G) and polar view (H). I. Louteridium dendropilosum (Daniel et al. 11784), with internal contents extruding via pores.