Poikilacanthus foliosepalus 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 : 146-147

Poikilacanthus foliosepalus T.F. Daniel , sp. nov.

Poikilacanthus foliosepalus differs from its congeners by the following combination of characters: short and few-flowered dichasiate spikes in leaf axils, elliptic calyx lobes 10–11 mm long and 2.7– 5 mm wide, red corollas 39–49 mm long that are externally pubescent with eglandular trichomes only, and four-aperturate pollen covered with densely spaced but mostly discrete insulae.

TYPE.— MEXICO. Oaxaca: Distr. Tlacolula, Mpio. Mitla, Tierra de Santo Pie de Cerro , 16°55’24.3”N, 96°24’21”W, 1673 m, selva baja caducifolia, 29-VII-2009 (flr) , H. Hernández O. 326 (holotype: MEXU!; isotypes: CAS!, SERO!).

Perennial herb to shrub to 8 dm tall; young stems subquadrate and 4-sulcate, evenly pubescent with erect to flexuose eglandular trichomes 0.2– 0.9 mm long. Leaves ascending to appressed, petiolate, petioles to 5 mm long, blades ovate to elliptic (to obovate), 17–38 mm long, 11. 5–22 mm wide, 1.2–1.7 × longer than wide, emarginated to rounded to acute at apex, cuneate at base, surfaces and margin pubescent with cauline type trichomes (although sometimes antrorse) and with trichomes denser on abaxial surface, major veins yellowish and prominent, margin entire. Inflorescence of short dichasiate spikes in axils of leaves; spikes pedunculate, few-flowered, peduncles 2–4 mm long, pubescent like young stems, rachis evenly pubescent with erect to flexuose eglandular trichomes 0.05– 0.1 mm long; dichasia alternate (1 per node), 1-flowered, sessile. Bracts sessile, subfoliose, broadly elliptic to subcircular, 7–10. 5 mm long, 4–8 mm wide, rounded at apex, abaxial surface pubescent like leaves. Bracteoles narrowly elliptic to oblanceolate, 3–4. 5 mm long, 0.6– 0.8 mm wide, abaxial surface pubescent like bracts. Flowers subsessile (i.e., borne on pedicels to 1.5 mm long), mostly 2 per spike. Calyx 5-lobed, 12–13 mm long, lobes elliptic, 10–11 mm long, 2.7– 5 mm wide, acuminate-subcaudate at apex, abaxial surface ± prominently 3–5-veined, pubescent with flexuose to appressed eglandular trichomes 0.05– 0.3 mm long or nearly glabrous distally, margin conspicuously ciliate with flexuose eglandular trichomes to 1 mm long. Corolla red, 39–49 mm long, externally pubescent with flexuose eglandular trichomes 0.1– 0.4 mm long, tube only very gradually and ± inconspicuously expanded distally (throat ± indistinct), 23–28 mm long, narrow proximal portion 18–20 mm long, 3– 3.2 mm in diameter near midpoint, throat 4–10 mm long, upper lip 15–21 mm long, 2-fid at apex, lower lip 16–21 mm long, lobes 6–8 mm long, 3.5– 4 mm wide. Stamens 17–18 mm long, filaments glabrous distally, thecae parallel, subequally inserted, 3.5– 4 mm long, subequal in length, glabrous, with a rounded basal appendage 0.1– 0.2 mm long (lower theca with a larger appendage than distal theca); pollen subprolate to euprolate, 4-aperturate (see discussion), polar diameter 52–55 μm, equatorial diameter 38–43 μm, insulae densely spaced but mostly discrete (rarely 2 sharing a common wall). Style 33–42 mm long, stigma 0.2 mm long, lobes not evident. Capsule and seed not seen.

PHENOLOGY.— Flowering: July; fruiting: July.

DISTRIBUTION AND HABITAT.— Southern Mexico (central Oaxaca; Fig. 1 ); plants occur in tropical deciduous forest at an elevation of 1673 m.

CONSERVATION.— The sole known collection of Poikilacanthus foliosepalus was made in the eastern portion of the Valley of Oaxaca. This species remains known only from the type locality, where an unknown number of individuals occurs, and from which it was collected in 2009. No information is known as to the current status of this species or any possible threats. Therefore, according to IUCN (2017) guidelines, the species has to be assessed as Data Deficient ( DD) .

ILLUSTRATION.— Figure 9.

DISCUSSION.— Poikilacanthus foliosepalus has one of the two pollen types characteristic of Mexican and Central American species treated in Poikilacanthus Lindau ( Daniel 1991, 1998), that is, with four or more apertures and the entire surface covered with discrete “insulae” consisting of gemmate regions enclosed by thick, smooth marginal walls ( Fig. 4D, E ). Pollen of Hernández O. 326, examined with both scanning and light microscopy, appears to have four apertures, but it is possible that some of the grains might have five.

Pollen appears to offer the only distinction between Poikilacanthus and Justicia (e.g., Daniel 1991, 1998). Recent molecular phylogenetic studies of Justicieae reveal that Poikilacanthus is polyphyletic, with species placed in several lineages among the large, diverse, and monophyletic clade of New World justicioids ( Kiel et al. 2017). Until such time as a comprehensive revision of all justicioids based on both molecular and morphological data has been completed, it seems reasonable to postpone generic/nomenclatural realignments and to maintain Poikilacanthus .

This species is distinctive among Mexican and Central American Poikilacanthus ( Daniel 1991, 2010) by its wide and somewhat leafy calyx lobes (vs. up to 1.5 mm wide in the other species). A species of Ruellia (Ruellieae) with similar subfoliose calyx lobes was recently described by Daniel (2008) from Guerrero. Poikilacanthus foliosepalus also appears to be unique among its Mexican and Central American congeners by the four-aperturate (vs. five- or more-aperturate) pollen ( Daniel 1998, 2010).

Figures

FIGURE 1. Map of southern Mexico (and northern Central America, shaded) with distributions of Carlowrightia yucatanensis (Yucatán), Justicia zapoteca (Oaxaca), Poikilacanthus foliosepalus (Oaxaca), and P. pochutlensis (Oaxaca).

FIGURE 9. Poikilacanthus foliosepalus (from Hernández O. 326). A. Node with leaves, inflorescence, and flower. B. Bract. C. Bracteole. D. Calyx lobe. E. Distal portion of stamen with bithecous anther. Drawn by Sean Edgerton.

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.