Phoradendron leucarpum
Phoradendron villosum
American mistletoe, oak mistletoe
oak mistletoe, Pacific mistletoe
green, grayish green, or yellowish green, hairy, hairs simple or stellate, white or yellow, becoming glabrate;
internodes terete, 8–59 × 1–3 mm.
green or olive green, grayish from pubescence, hairy, hairs stellate, becoming hirtellous to glabrate;
internodes terete, 1.5–3.8 × 1–3 mm.
bright green, yellowish green, or grayish green, well developed, hairy, hairs simple or stellate;
petiole 3–8 mm;
blade obovate, spatulate, ovate, ovate-elliptic, or nearly orbiculate, 14–48 × 8–30 mm, thin to thick and rigid, base cuneate to obtuse, apex rounded;
basal phyllotaxy transverse.
green or olive green, grayish from pubescence, stellate-hairy;
blade obovate-elliptic to orbiculate, 13–45 × 9–22 mm, thin to thick and fleshy, base subtruncate to acute, apex rounded to acute;
basal phyllotaxy transverse.
petals 3, 1 mm.
petals 3–4, 1 mm.
white, oblong to globose, 3–6 × 2–5 mm, glabrous.
white to pink, oblong to globose, 3 × 3 mm, puberulent below petals.
inflorescences 10–80 mm, hairy, hairs simple or stellate;
peduncle with 1 internodes, 2–4 mm;
fertile internodes 2–7, each (15–)29–39(–62)-flowered, triseriate, becoming irregular, flowers 1–10 per column.
inflorescences 10–80 mm, stellate-hairy;
peduncle with 1 internode, 2–4 mm;
fertile internodes 2–5, each (14–)26(–44)-flowered, triseriate, becoming irregular, flowers 2–7 per column.
inflorescences 10–80 mm, hairy, hairs simple or stellate;
peduncle with 1 internode, 2–4 mm;
fertile internodes 2–6, each (4–)6–11(–20)-flowered, triseriate, flowers 1–3 per column.
inflorescences 10–80 mm, stellate-hairy;
peduncle with 1 internode, 2–4 mm;
fertile internodes 2–3, each (6–)11(–24)-flowered, triseriate, flowers 1–4 per column.
Phoradendron leucarpum
Phoradendron villosum
J. Kuijt (2003) used the name Phoradendron serotinum, based on the name Viscum serotinum Rafinesque (1820), not P. leucarpum, which is based on the earlier name by the same author, V. leucarpum (1817). A proposal to conserve the later name (D. L. Nickrent et al. 2010b) was not accepted, thus the name P. leucarpum has priority.
Phoradendron leucarpum has a convoluted taxonomic history, reflecting not only various species concepts but also complex evolutionary and ecological processes. Among the 234 species of Phoradendron, J. Kuijt (2003) recognized subspecies only in P. leucarpum (as P. serotinum). In addition to the typical subspecies from eastern Texas eastward, they are subsp. augustifolium from Mexico, subsp. macrophyllum from eastern Texas through New Mexico and Arizona to California and Oregon, and subsp. tomentosum, with about the same distribution as subsp. macrophyllum but also extending into Mexico. Kuijt noted that in some geographic areas, such as east-central Texas, the putative subspecies show a continuum of morphological intergradation.
A population genetic and morphometric study of this complex was undertaken by A. K. Hawkins (2010). Principal component analyses using the characters that J. Kuijt (2003) considered to be diagnostic of the subspecies, such as leaf size, color, and venation, as well as the type and density of hairs present on young vegetative and reproductive tissues, in addition to host species, did not result in clusters corresponding to the four described subspecies. Moreover, FST analyses of microsatellites showed significant interpopulational differentiation that did not match the subspecies that Kuijt recognized. Because morphological and molecular analyses show that subspecies, at least as defined by Kuijt, cannot be differentiated in Phoradendron leucarpum, no subspecies are accepted here.
Phoradendron leucarpum is the only species of the genus found east of Texas. It parasitizes over 60 species of native and introduced trees, especially Acer, Fraxinus, Juglans, Nyssa, Platanus, Populus, Quercus, Salix, and Ulmus.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Subspecies 3 (2 in the flora).
Phoradendron villosum was treated by J. Kuijt (2003) as a synonym of P. serotinum subsp. tomentosum (= P. leucarpum in this treatment), but P. villosum has a different, non-overlapping flowering time, shorter stem internodes, and hairy berries. In addition, P. villosum averages fewer pistillate inflorescence fertile internodes than P. leucarpum. Molecular studies by V. E. T. M. Ashworth (2000, 2000b) showed that P. villosum did not form part of the strongly supported P. leucarpum clade. For these reasons, they are here considered distinct species, as was done by D. Wiens (1964).
Subspecies flavum (I. M. Johnston) Wiens, distinguished by its yellow leaf hairs, is found in Coahuila and Durango, Mexico.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Hairs on young stems, leaf blades, and inflorescences of one type, uniformly distributed and of similar lengths; pistillate inflorescence internodes each (7–)12(–24)-flowered; California, Oregon. | subsp. villosum |
1. Hairs on young stems, leaf blades, and inflorescences of two types, some in dense clusters, relatively longer, others uniformly distributed, relatively shorter; pistillate inflorescence internodes each (6–)8(–12)-flowered; Arizona, New Mexico, Texas. | subsp. coryae |
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