Macrosolen zamboangensis (Loranthaceae), a new mistletoe species from Zamboanga Peninsula, Philippines

From Firenze University Press Journal: Journal of Plant Taxonomy and Geography (Webbia)

Kean Roe Mazo, Department of Forest Biological Sciences, College of Forestry and Environmental Science, Central Mindanao University

Daniel L. Nickrent, Plant Biology Section, School of Integrative Plant Science, College of Agriculture and Life Science, Cornell University

Pieter B. Pelser, School of Biological Sciences, University of Canterbury

Macrosolen (Blume) Rchb. (Loranthaceae; Elytranthinae) is a genus of hemiparasitic epiphytes represented by at least 25 (Vidal-Russell and Nick-rent 2008), but perhaps as many as 40 (Tagane et al. 2017) species. It is recognized by having spikes or racemes with decussate pairs of 6-merous flowers that are each subtended by one bract and two bracteoles, petals that are fused to the middle or higher, reflexed corolla lobes, and 4-locular anthers (Barlow 1997, Tagane et al. 2017). Macrosolen is distributed in southern Asia and the Malesian region, with a center of diversity in Borneo (Barlow 1997). In the Philippines, there are seven currently recognized Macrosolen species, two of which are endemic (Pelser et al. 2011 onwards). The island of Mindanao is a center of diversity for the genus as all seven Philippine species can be found there (Pelser et al. 2011 onwards). During field work in the municipality of Leon B. Postigo, Zamboanga del Norte (Zamboanga Peninsula, Mindanao), an unknown species of Macrosolen was documented and collected. Initially, it was identified as M. melintangensis (Korth.) Miq. using Barlow’s (1997) taxonomic key, but further investigation revealed several morphological differences.

Macrosolen melintangensis is a taxonomically challenging species complex with unclear species boundaries. Vegetatively, it is characterized by having opposite, petiolate, ovate, medium sized, bifacial leaves. It has few-flowered racemes with bracteoles that are nearly free, and slender corollas that are mostly 20–30 mm long and usually have weakly developed wings (Barlow 1995). Most recently Barlow (1995, 1997) used a broad delimitation of M. melintangensis, in which he subsumed a large number of species recognized by Danser in his taxonomic treatments of Macrosolen (Danser 1931, 1934, 1935, 1941): M. bellus Da nser, M. floridus Da nser, M. javanus Danser, M. lowii (King) Tiegh., M. suma-tranus Danser, and M. urceolatus Danser. Barlow (1995) also provisionally included M. demesae (Merr.) Danser and M. tenuiflorus Danser as synonyms. As a result, M. melintangensis is currently circumscribed as a quite polymorphic species with a large distributional area (Borneo, Cambodia, Java, Malay Peninsula (including Singapore), Philippines, Sumatra and Thailand; Barlow 1995). Barlow interpreted the much narrower species delimitation of this complex by Danser (1931, 1934, 1935, 1941) as a segregation into “local races” (Barlow 1995: 28) and concluded that these do not merit recognition at the species level, because of the absence of “sharp morphological discontinuities” among them. However, Barlow (1995, 1997) did not present data in support or this view, nor provide a more detailed discussion.

Further, our current study in search of the identity of the Zamboanga Macrosolen plants revealed morphological patterns that suggest that more than one species should be recognized within the M. melintangensis complex (see Discussion), although more detailed studies are required to deter-mine their exact number. In this study, we compare the Macrosolen plants from Zamboanga with M. melintangensis sensu Barlow (1995, 1997), the putative species that Danser (1931, 1934, 1935, 1941) recognized within this species complex, as well as other species that display morphological similarities. We conclude that the Zamboanga plants are best considered as a new species under the unified species concept (De Queiroz 2007), because they are morphologically different from all members of the M. melintangensis species complex.


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