Pentacalia basitruncata J. Calvo & H. Beltrán, 2018

Calvo, Joel & Beltrán, Hamilton, 2018, Two new species of Pentacalia (Senecioneae, Compositae) from Peru, Phytotaxa 357 (4), pp. 284-290 : 284-288

1. Pentacalia basitruncata J. Calvo & H. Beltrán , sp. nov. ( Fig. 1 )

Type: — PERU. Junín: provincia Huancayo, distrito Pariahuanca , entre Pahual y Chilifruta, 18 L 510222 E 8672446 S [12º00’32”S 74º54’22”W], 3300 m, 11 Aug 2017, H. Beltrán 8544 (holotype: USM 302025 ; isotypes: HUT, MO, QCA) .

Pentacalia basitruncata can be readily distinguished by the combination of the following characters: synflorescence mainly terminal, capitula disciform, sessile, clustered, abaxial leaf surface densely and persistently white-lanate, leaf margins dentate, and leaf lamina bases plainly truncate.

Scandent woody vines. Stems terete, furrowed, with evanescent arachnoid-floccose indumentum, solid. Leaves alternate, chartaceous, not reflexed; lamina oblong-elliptic, 9.5–13.5 cm long, 4–6 cm wide, acute to acuminate, truncate at base, dentate (teeth 1–2.2 mm deep), plane, adaxial surface glabrous except for some arachnoid trichomes on the midrib, not lustrous, and with secondary venation weakly conspicuous, abaxial surface densely and persistently white-lanate, with protruding secondary venation; petiole 1–1.5 cm, arachnoid-floccose to lanate. Synflorescences mostly terminal, narrowly paniculiform-thyrsoid, with the main axis fractiflex, capitula somewhat clustered at the distal part of each lateral synflorescence branch, with reduced linear bracts at the base of each synflorescence branch; synflorescence branches with evanescent arachnoid-floccose indumentum; capitula disciform, sessile, without bracteoles or only a few. Involucre cylindrical, 3.7–4.2 mm long, 2.5–3 mm wide, with arachnoid indumentum at the base. Involucral bracts 8(–9), 3.3–4 mm long, 0.8–1.2 mm wide, glabrous, herbaceous; supplementary bracts 6–8, 0.9–1.8 mm long, ca. 0.5 mm wide, a quarter as long as the involucral bracts, with arachnoid trichomes. Female florets 5, tubular, 3.6–3.9 mm long, (3–)4-lobed, with lobes filiform, ca. 1.3 mm long, yellowish-green; bisexual florets 8–11, 3.9–4 mm long, 5-lobed, with lobes subulate, ca. 1.4 mm long, yellowish-green. Anther bases shortly sagittate, ca. a third as long as the filament collar. Style-branches truncate with a crown of sweeping trichomes. Achenes ca. 1 mm long, 0.5 mm wide, cylindrical, ribbed, blackish, glabrous; pappus 4.1–4.3 mm long, barbellate, white. Chromosome number: unknown.

Distribution and habitat: —This species is only known from the type locality, in the district of Pariahuanca (Junín Department; figure 2). It thrives in remnants of humid montane forest, around elevations of 3300 m. Some common species of the vegetation are Coriaria ruscifolia Linnaeus (1753: 1037) , Dendrophorbium yalusay (Cabrera 1950: 112) Jeffrey (1992: 69) , Desfontainia spinosa Ruiz & Pavón (1799: 47) , Nordenstamia tovarii ( Robinson & Cuatrecasas 1992: 413) Nordenstam (2006: 22) , and Senecio betonicifolius Candolle (1838: 422) .

Phenology: —It was collected in bloom in August.

Etymology: —The epithet basitruncata refers to the distinctive truncate base of the leaf lamina.

Discussion: —This new species is easily distinguishable by the morphology of its leaves. These are dentate, clearly truncate at the base, and covered by a dense and persistent white-lanate indumentum beneath. The synflorescences are mainly terminal, and the capitula are disciform, sessile, and clustered. They have ca. 5 peripheral female florets and 8–11 bisexual florets. Further collections are required to complete the description of the achenes.

Pentacalia basitruncata keys out in the group of P. herzogii (Cabrera 1952: 202) Cuatrecasas (1981: 246) [= P. marinii (Cabrera 1954: 590) Cuatrecasas (1981: 248) , syn. nov.], and P. oronocensis (Candolle 1838: 423) Cuatrecasas (1981: 248) [= P. megaphlebia (Greenman & Cuatrecasas in Cuatrecasas 1953: 288) Cuatrecasas (1981: 248), syn. nov.]. It differs from P. herzogii in the leaf base shape (truncate vs. obtuse to rounded) and the leaf margin (dentate vs. remotely mucronate-denticulate or entire). Pentacalia herzogii has been consistently separated from P. marinii , described from the Peruvian Cusco Department, in account of its mucronate-denticulate leaf margins and its involucre not completely covered by indumentum (Cabrera 1954, 1985, Robinson & Cuatrecasas 1993). On the other hand, Gynoxys discolor Rusby (1907: 398) from Bolivia has been accepted as a synonym of P. marinii (Cabrera 1985 under Senecio marinii, Beck & Ibáñez 2014 under P. marinii ) because of its entire leaf margins and despite the involucres only having indumentum at the base. It has to be noted that in 2014 the epithet discolor was not available for use in Pentacalia due to the existence of Pentacalia discolor ( Swartz 1788: 114) Robinson in Proctor (1982: 311). In our opinion, the three taxa should be treated as the same taxonomic entity, P. herzogii being the priority name. It is quite a variable species as it can be noticed on the specimen Lewis 39710 ( US 01844836), collected really close to the type locality of P. herzogii . Lewis’s collection has both entire and mucronate-denticulate leaves, as well as capitula with floccose indumentum covering the whole involucre or restricted at the base. Likewise, around the Bolivian provinces of Nor and Sud Yungas, it is frequent to find plants with leaves entire ( US 01844857) or distantly mucronate-denticulate ( US 01844829). Species with entire leaf margins that eventually have remotely mucronate-denticulate margins, or vice versa, are not rare in Pentacalia . This has also been observed in P. andrei ( Greenman 1938: 797) Cuatrecasas (1981: 243) , P. millei ( Greenman 1938: 809) Cuatrecasas (1981: 248) , and P. oronocensis .

From Pentacalia oronocensis , the new species can be separated by its truncate leaf base (cuneate to rounded in P. oronocensis ), dentate leaf margins (remotely mucronate-denticulate or entire in P. oronocensis ), and the type and color of the involucre indumentum. Pentacalia basitruncata has involucres with whitish arachnoid indumentum only at the base, while in P. oronocensis they are completely covered by lanate ochraceous indumentum. The color of the abaxial leaf surface indumentum is also useful (rather ochraceous in P. oronocensis vs. whitish in P. basitruncata ). Pentacalia oronocensis has a wide distribution from southern Ecuador to Bolivia. It should be noted that the collection Holm- Nielsen 29720 (see US 01844550) cited in Tropicos (2018) as P. oronocensis from Carchi Province (northern Ecuador) actually corresponds to P. disciformis ( Hieronymus 1900: 72) Cuatrecasas (1981: 245) .

It is also important to note that P. megaphlebia is here considered a synonym of P. oronocensis . The diagnostic characters stated by Greenman & Cuatrecasas in Cuatrecasas (1953) fit well within the variability displayed by P. oronocensis along its wide distribution. Therefore, the synonymy of P. oronocensis is expanded to include the following names: Senecio baccharidiflorus Rusby (1907: 397) , Senecio cuzcoensis Cabrera (1944: 196) , Senecio ramonii Cuatrecasas (1951: 53) , and P. megaphlebia .

Figures

FIGURE 1. Holotype of Pentacalia basitruncata (USM 302025).