Erythroxylum ulei var. escalerense D. M. White, 2020

White, Dawson M., 2020, A new variety of Erythroxylum ulei from the Cordillera Escalera of Peru (Archerythroxylum, Erythroxylaceae), Phytotaxa 449 (3), pp. 279-286 : 281-285

Erythroxylum ulei var. escalerense D. M. White , var. nov.

Type:— PERU. Loreto: Cordillera Escalera, Provincia Alto Amazonas, Distrito Balsapuerto: Bosque a orillas del Río Cachiyacu , 267 m, 76º36’15.7” W, 5º53’22” S, 18 Sept. 2013 (fl, fr), Marcos Ríos, Tony Mori, David Neill, Luis Torres, Corine Vriesendorp 3080 (holotype: USM! , isotypes: AMAZ!, ECUAMZ, F!, NY!, US!, MO!, MOL! , Figs. 1 , 2 ).

Diagnosis: — E. ulei var. escalerense is similar to E. ulei and E. schunkei in having stipules with two elongated lateral setae, evergreen leaves with foliicolous lichens, and ovoid fruits, but differs by its smaller (26–53 mm long × 8–14 mm wide), narrowly elliptic to lanceolate leaves which are not strongly bifacial and revolute margins ( Table 2 ).

Description: — Shrub 1.5 m, Branchlets compressed, 1.0 mm by 1.0– 1.3 mm wide, greenish-brown in young branchlets, drying-reddish brown, lenticels elliptic. Cataphylls persistent, occasionally forming ramenta near ends of shoots, similar to stipules, chartaceous. Foliar stipules distichous, erect, triangular, 1.2–1.8 mm long, membranous, nonstriate, green, drying light brown, apex obtuse, with 2 erect setae 0.5 mm long extending from two dorsal ridges, third apical seta shorter and usually absent margin entire, scarious in young stipules. Leaves persistent, distichous, short-petiolate, laminas narrowly elliptic, 26–53 mm long, 8–14 mm wide, base cuneate, apically acute to obtuse, mucronulate with mucron 0.2–0.5 mm, the upper surface smooth, dark green, adaxial midrib light green, sulcate to slightly raised, the lower surface light green, not bilineate or with areole, mixed eucamptodromous venation with 20–40% of secondary nerves forming brochiodromous arches, the secondary nerves 6–9, more distinct on upper surface than lower surface. Petiole 2.5–3.2 mm long, adaxially canaliculate, drying dark brown. Flowers few, axillary, sequentially one per node. Bracteoles 0.9–1.4 mm long, triangular ovate, 1-keeled, apex acute, 1-setulose, seta 0.2–0.4 mm. Pedicel 2.8–3.1 mm long in flower, 5.0 mm long in fruit, diameter increasing in size from 0.4 mm at base to 0.6 mm at tip, 5-ribbed. Calyx 1.5 mm long, divided to 2/3 its length, the lobes 1 mm long, triangular to lanceolate, slightly acuminate at apex. Petal lamina oblong, slightly concave, ca. 2.0 mm long (excluding claw), 1.0 mm wide, the claw ca. 1.0 mm long, the ligule bilobed, 1.1–1.7 mm long, forming tube around stamens, with labiate anterior auricle at base of lobes. Staminal tube shorter than calyx, ca. 1.0 mm tall, margin smooth. Brachystylous flowers: filaments 2.5–2.8 mm long, the anthers ovate to elliptic, ca. 035 mm long; styles 1.0– 1.2 mm long, free; stigmas capitellate, 0.2–0.3 mm long. Dolichostylous flowers: unknown. Ovary oblongoid, 1.0– 1.1 mm long, equal or slightly longer than staminal tube. Drupe elliptic or slightly ovate, tapering to obtuse apex, purple, the endocarp ovoid-elliptic, semiterete, apex acute and trigonous, 6.0–7.0 mm long and 4.0 mm in diameter, 3-locular, two of the locules empty and almost obsolete, the fertile locule elliptic in cross-section, the endosperm occupying>80% of area.

Etymology: —The varietal epithet is derived from the collection locality in the hope that it will draw attention to the biological diversity of the understudied Cordillera Escalera of Peru.

Distribution: —Cordillera Escalera, Loreto, Peru (only one locality). The shrub was found at the forest’s edge on the sandy, seasonally-inundated bank of the Rio Cachiyacu ( Fig. 1a ) by the Field Museum of Natural History’s Rapid Inventory team. No seedlings were found but there was copious fruit set with normal embryo and endosperm tissue development in this single individual.

Comments: —While field biologists and ecologists can frequently identify Erythroxylum to the genus level, specific determination in this group is significantly more challenging due to the importance of a handful of morphological characters based primarily on stipule, cataphyll, leaf, flower and fruit organs. Upon viewing photos of E. ulei var. escalerense , it was hypothesized to be an undescribed due to the color, size, and shape of leaves; quite distinct from E. ulei or any other Andes/ Amazon region Erythroxylum (Pers. obs.; D. Neill & A. Jara Muñoz, pers. comm.). However, other organs, including the stipules, as well as flower and fruit morphology are within the variation exhibited by E. ulei . The other similar species, E. schunkei , a nearby regional endemic from the lowland forests of the Ucayali Department of Peru, is easily distinguished from E. ulei by the stout, persistent, and long (2–5 mm) lateral stipular setae. The leaves of E. schunkei are more similar to E. ulei in their size, shape, and bifacial coloring not seen in E. ulei var. escalerense ( Table 2 ; Plowman 1984). If more E. ulei var. escalerense individuals were examined and found to have close morphology to the type specimen, this taxon could warrant elevation to the level of species.

The molecular phylogenomic hypothesis also supports the close relationship of E. ulei to E. ulei var. escalerense with strong support, with the Escalera variety being more closely related to the E. ulei sample (501) from Bolivia than to the E. ulei sample (509) from Colombia ( Figure 3 ). Erythroxylum schunkei is sister to this species, a close relationship hypothesized by Plowman (1984) based on its close morphology. Given the large geographic range of E. ulei and the very restricted range of E. ulei var. escalerense , it is plausible that the paraphyly of E. ulei with respect to divergent morphology presented by E. ulei var. escalerense is manifesting from incipient peripatric speciation. It is also possible there is directional gene flow from E. ulei into this population in the Cordillera Escalera. I have observed specimens of E. ulei from the seasonally dry forests west and south of Tarapoto, San Martín, Peru, but none from the wet forests of the Cordillera Escalera.

In his intrageneric classification system, O. E. Schulz (1907) placed E. ulei and four other species into the small section Leptogramme based on the presence of indistinctly striated stipules. Considering the presence or absence of these striations is a very prominent character for several of his other sections, sect. Leptogramme may have been created to accommodate the residuals. My expanded phylogenetic reconstruction of Erythroxylum reveals the other four species in this section are all distant relatives ( E. pulchrum Saint-Hilaire (1829: 94) , E. passerinum von Martius (1840: 386) , E. ovalifolium Peyritsch (1878: 135) , E. substriatum Schulz (1907: 62) ; White et al. 2019) However, overlooking the striations, Plowman (1984) places E. ulei and E. schunkei in sect. Archerythroxylum , a large section of ca. 65 species characterized by unstriated stipules, perfect flowers, and free styles ( Schulz 1907). Indeed, the close relatives to the E. ulei clade are all Archerythroxylum species from the western Amazon and Andean region ( White et al. 2019). Therefore, our phylogenetic analysis supports Plowman (1984) and, pending formal revision of all intrageneric sections, E. ulei and this new variety should be classified in section Archerythroxylum .

Lastly, it must be noted that the live-plant photograph presented in Figure 1d shows the presence of short, velutinous hairs on the fruits. As the Erythroxylaceae are described as glabrous, this is a mysterious observation. The pubescence was not present on the dried material I examined, which was preserved in alcohol in the field and subsequently ovendried, which suggests the ‘hairs’ are fungus. However, it is also possible that pubescence is an infrequent character in Erythroxylum that is always lost during herborization. Any pubescence should be noted and investigated if observed on this or any other member of the Erythroxylaceae .

Figures

FIGURE 1. E. ulei var. escalerense A) Habitat of E. ulei var. escalerense, Rio Cachiyacu at base of the Cordillera Escalera range, Loreto, Peru. B) Flowering and fruiting branchlet. C) Leaves. Bar = 10 mm. D) Fruit detail, notice apparent pubescence. E) Young foliar stipule; mature stipules are larger but frequently lose setae. F) Flower detail. Bar = 10 mm. Photo credits: A=Alvaro del Campo; B,D,E = David Neill; C,F=Dawson White.

FIGURE 2. Habit of E. ulei var. escalerense. Bar = 50 mm.

FIGURE 3. Phylogenetic relationships of E. ulei and close relatives based on ASTRAL summary tree of 544 gene trees. This clade was extracted from a larger phylogenetic inference including 203 Erythroxylaceae species. Node labels show local posterior probability; branch lengths are arbitrary.