Analysing the morphological variation of the Galápagos mistletoe Phoradendron berteroanum (DC.) Griseb. using herbarium specimens

The hemiparasitic mistletoe Phoradendron berteroanum (DC.) Griseb. in the Galápagos shows remarkable morphological variation suggesting either clinal or abrupt geographical variation. Eight vegetative and floral traits were measured from 68 herbarium specimens to assess patterns of morphological variation in P. berteroanum. Univariate and multivariate analyses comparing the traits by altitude, island, host, and vegetation cover were performed. Leaf size and internode length were larger at mid-elevations, while the number of floral segments decreased with altitude. Flower number varied by host, notably higher on Scalesia baurii B.L.Rob. & Greenm. from Pinzón Island. No evidence of unique island populations was found, so there is no morphological support for considering more than one species of mistletoe in the Galápagos. These results reveal how P. berteroanum responds to local environmental conditions across the Galápagos.