Phoradendron longicaule Kuijt & V. W. Steinm., 2016

Kuijt, Job & Steinmann, Victor W., 2016, Phoradendron longicaule (Viscaceae): a new species from Michoacán, Mexico, Phytotaxa 275 (2), pp. 181-185 : 181-184

Phoradendron longicaule Kuijt & V. W. Steinm. , sp. nov. ( Figs. 1 and 2 ).

Similar to P. nudum but differs by having longer vegetative internodes, expanded albeit highly reduced leaves, and 3 or 4 pistillate flowers per fertile bract; similar also to P. teretifolium from which it differs by having a pendulous habit, longer vegetative internodes, and 3 or 4 pistillate flowers per fertile bract.

Type:— MEXICO. Michoacán: Mpio. La Huacana , Sierra las Cruces, ca. 5 km al oeste-noroeste de Los Ranchos, sobre la vereda a Los Cueramos, 18°42’45” N, 102°04’00” W, 500 m, sobre Acacia cochliacantha , escasa en bosque tropical caducifolio, 1 May 2004 [♀], V. W. Steinmann 4264 (holotype MEXU!; isotypes ARIZ!, RSA!, MICH!, MO!, NY!) .

Large, profusely branched, bright green, pendulous plants with stems to 1 m long, glabrous throughout. Internodes slender and much elongated, grayish when young, 3–6 cm long, 2–3 mm thick, terete, deeply grooved when dry, bearing innumerable stomata; basal and intercalary cataphylls absent. Basal phyllotaxy median. Leaves paired, early caducous, fleshy, 1–5 × 1.5 mm, more or less cylindrical or slightly dorsoventrally flattened, apex rounded; prophylls yellow, evident, blunt, with smooth, fleshy margins; basal foliar organs median. Dioecious; inflorescences axillary and eventually also in axils of prophylls, mostly on older growth. Staminate inflorescences golden yellow, often in small clusters, 3–4 mm long, with a terminal, raised crest, peduncle extremely short (0.5 mm), followed by one fertile internode; flowers 3 per fertile bract, apical flowers 2/1, distal flowers 1/2, yellow, triseriate, anthers white, biloculate, with two conspicuous pores. Pistillate inflorescence of similar size, peduncle as in the staminate, usually followed by one fertile internode; flowers yellow, 3 or 4 per fertile bract, triseriate; sometimes with an additional, very short, 2-flowered terminal internode. Fruits globular to somewhat short-obpyriform, 3(4) per fertile bract, 2.5 × 2 mm, the distal 0.5 mm consisting of prominent, more or less closed petals bright reddish orange at maturity. Seeds 3 × 2 mm, broadly lanceolate, slightly notched at one end, straw-colored when dry.

Distribution, habitat and phenology:— Phoradendron longicaule is known from three collections made within the Infiernillo-Zicuirán Biosphere Reserve of southern Michoacán, Mexico, at elevations of 400 to 500 m. This area forms part of the lower Balsas Depression and is considered to be an important center of endemism ( Guevara-Fefer & Rzedowski, 1980). It grows in tropical deciduous forest, and hosts include Acacia cochliacantha Humb. & Bonpl. ex Willdenow (1806: 1081) , Apoplanesia paniculata Presl (1831: 64) , and an unknown species of Fabaceae subfamily Mimosoideae . All three known localities occur within four kilometers of each other, with a total area of occurrence of less than 10 km 2; however, its actual distribution is likely greater, and much of the surrounding area has not been surveyed.

Phoradendron longicaule is the only known species of the genus endemic to Michoacán. Although a detailed assessment of its conservation status is lacking, its limited distribution and apparent host specificity to a few species of Fabaceae suggest that it is vulnerable if not endangered following IUCN Red List criteria ( IUCN, 2001). Flowering and fruiting occur both in the dry and rainy seasons, with flowers collected in January, May and September, and fruits in May and September.

Etymology:—The specific epithet “ longicaule ” refers to the long pendulous stems with elongated internodes.

Additional specimens examined (paratypes):— MEXICO. Michoacán: Mpio. La Huacana, Sierra las Cruces , 5.5 km al oeste de Los Ranchos, sobre la vereda a la Barranca de la Vaca, 18°41’43”N, 102°04’02”W, 500 m, 29 January 2009 [♂], V. W. Steinmann 6584 ( ARIZ, IEB, MEXU, NY) ; Sierra Las Cruces, ca. 5.7 km (en línea recta) al suroeste de Nuevo Centro sobre una brecha que va a la base del Condémbaro, 18°43’46.3”N, 102°03’39.7”W, 410 m, en Apoplanesia paniculata , 11 September 2014 [♀], V. W. Steinmann & Y. Ramírez-Amezcua 7843 ( ARIZ, IEB, MEXU, MICH, MO, NY) .

Figures

FIGURE 1. Phoradendron longicaule Kuijt & V.W. Steinm. A. Habit; B. Young, pendulous shoot; C. Node with young and mature staminate inflorescence; D. Infructescence. A–C based on Steinmann 4264; D based on Steinmann & Ramírez-Amezcua 7843. Drawn by Job Kuijt.

FIGURE 2. Phoradendron longicaule Kuijt & V.W.Steinm.A. Habit; B. Close-up of shoot system; C. Staminate inflorescences; D.Young fruits on pistillate infructescences.A, C Steinmann 6584; B, D Steinmann & Ramírez-Amezcua 7843. Photos by Victor W. Steinmann and Yocupitzia Ramírez-Amezcua.