Pentacalia mikanioides J.Calvo, 2018

Calvo, Joel & Buira, Antoni, 2018, Two new species of Pentacalia (Compositae, Senecioneae) from northern Andes, Phytotaxa 364 (2), pp. 193-201 : 197-199

2. Pentacalia mikanioides J.Calvo , sp. nov. ( Fig. 4 )

Type: — ECUADOR. Zamora-Chinchipe: límite provincial Loja-Zamora, carretera antigua a Zamora , 03º58’56’’S 79º08’07’’W, 2620 m, J. Calvo & I. Arnelas JC 7698 (holotype: HUTPL 13587 ; isotypes: HUTPL 13588 , LOJA) .

Pentacalia mikanioides differs from the other disciform species with terminal, paniculiform-thyrsoid synflorescences and sessile capitula by its large, chartaceous leaves with shallowly dentate margins and tomentose stems.

Scandent woody vines. Stems terete, tomentose, becoming tomentulose as time passes, fistulous. Leaves alternate, chartaceous, only reflexed on the pendulous stems; lamina lanceolate to broadly lanceolate, 10–19 cm long, 4–10 cm wide, attenuate, rounded, shallowly dentate, with callus-like teeth, plane or almost so, adaxial surface with sparse, deciduous arachnoid-floccose indumentum, not lustrous, and with secondary venation conspicuous, abaxial surface with deciduous, sparse arachnoid-floccose indumentum that remains only on the midrib and secondary veins with age, and protruding secondary venation; petiole 1.5–2.6 cm, tomentose-arachnoid. Synflorescences terminal, broadly paniculiform-thyrsoid, with each lateral synflorescence branch clearly patent on the main axis, congested, with reduced linear bracts at the base of each synflorescence branch; synflorescence branches tomentose-arachnoid; capitula disciform, numerous, sessile, without bracteoles or only a few. Involucre cylindrical, 3.5–4 mm long, 2–2.5 mm wide, with arachnoid indumentum at the base. Involucral bracts 8, 3.2–3.4 mm long, 0.7–1.1 mm wide, with scattered trichomes, herbaceous; supplementary bracts 5–7, 0.7–1.6 mm long, ca. 0.4 mm wide, a quarter as long as the involucral bracts, slightly arachnoid. Female florets 2–3, tubular, 2.7–3 mm long, 4–5-lobed, whitish; bisexual florets 8–10, 3.6–4.2 mm long, 5-lobed, whitish. Anther’s base sagittate, as long as or longer than the filament collar. Style-branches truncate with a crown of sweeping-hairs. Achenes 1.6–1.8 long, 0.5 mm wide, cylindrical, blackish, glabrous, ca. 9-ribbed; pappus 3.4–3.5 mm long, barbellate, whitish. Chromosome number: unknown.

Distribution and habitat: —So far, this species is only known from a montane forest in the old road Loja-Zamora, near the provincial limit of their namesake provinces on the eastern slope of the range ( Fig. 5). It grows at ca. 2600 m, along with Pentacalia dorrii Robinson & Cuatrecasas (1993: 286) and P. sevillana ( Cuatrecasas 1954: 45) Cuatrecasas (1981: 250) .

Phenology: —Seen in bloom in December.

Etymology: —This new species greatly resembles a Mikania species, especially the living plants in the field. For that reason, it is named as such.

Discussion: — Pentacalia mikanioides is characterized by displaying terminal, paniculiform-thyrsoid synflorescences, disciform capitula with 2– 3 female florets and 8–10 bisexual florets, which are clustered and sessile,

and by having large, chartaceous, shallowly dentate leaves with deciduous indumentum on both faces, and tomentose stems becoming tomentulose as time passes.

Pentacalia millei ( Greenman 1938: 809) Cuatrecasas (1981: 248) , P. oronocensis ( Candolle 1838: 423) Cuatrecasas (1981: 248) , and P. zamorana Robinson & Cuatrecasas (1993: 291) are three species belonging to the same group (i.e., terminal synflorescence, disciform, sessile capitula), that thrive in the same region as the new species. Morphologically, the most similar species is P. millei because the leaves also have deciduous arachnoid indumentum beneath. However, the leaves of this latter species are somewhat fleshy, drying coriaceous (vs. chartaceous), entire or with remote mucronate denticulations (vs. shallowly dentate, with callus-like teeth), and have conspicuous, closely reticulate tertiary venation on both faces and protruding secondary venation beneath (vs. inconspicuous tertiary venation above and not protruding secondary venation beneath). The stems are arachnoid-floccose in P. millei whereas in P. mikanioides they are tomentose and become tomentulose as time passes. Another difference between these two species is leaf size, 3.5–6(–10) cm long in P. millei vs. 10–19 cm long in P. mikanioides . Pentacalia oronocensis and P. zamorana also have leaf laminas considerably smaller than P. mikanioides . Moreover, P. oronocensis has a persistent, lanate indumentum on the abaxial leaf surface, as well as on the involucres. With regard to P. zamorana , this species also differs in its essentially glabrous and coriaceous leaves with far fewer teeth on the margins.

Another species with terminal synflorescences, disciform, sessile capitula, and large leaves is P. mucronatifolia Robinson & Cuatrecasas (1993: 295) , known from Luya Province (Amazonas Department, northern Peru). Pentacalia mikanioides can be differentiated from it by the apex leaf shape(attenuate vs.rounded and cuspidate in P.mucronatifolia ), leaf margin (shallowly dentate vs. with remote mucronate denticulations or entire in P. mucronatifolia ), and leaf consistency and venation (chartaceous, inconspicuous tertiary venation above vs. coriaceous, conspicuous, closely reticulate tertiary venation above in P. mucronatifolia ).

In Colombia only one species displays disciform, sessile capitula arranged in paniculiform-thyrsoid synflorescences, i.e., P. hachana ( Cuatrecasas 1944: 25) Cuatrecasas (1981: 246) . However, its leaves are smaller than those of P. mikanioides (5–9 cm vs. 10–19 cm long) and have conspicuous, closely reticulate tertiary venation. Synflorescences in P. hachana are also shorter and laxer than those of P. mikanioides .

Figures

FIGURE 4. Pentacalia mikanioides.A.Adaxial surface of a mature leaf. B. Adaxial surface of a young leaf. C.Abaxial surface of a young leaf. D. Detail of the capitula. E. Detail of the stem indumentum. F. Terminal synflorescence.