Morphological and Physiological Differentiation of Phoradendron Populations in Texas

Abstract

Investigation of the morphology and physiology of the mistletoe, Phoradendron tomentosum subsp. tomentosum, in Texas reveals that the subspecies is differentiated into at least two ecological races, one in north central Texas, the other in south central Texas. The races differ in leaf length/width ratio, fruit diameter, seed set, spike internode length, freeze tolerance, and flavonoid patterns. Clines occur in leaf length/width ratio and fruit diameter between the races, and these characteristics are negatively correlated. The northern race generally exhibits greater freeze tolerance than the southern race. Field observations, herbarium specimens, and a collection of fresh specimens from northeastern Mexico indicate that a third race in the subspecies may exist there. Racial variation within the subspecies appears to permit it to occupy a diversity of habitats. Morphological and physiological patterns within the two Texas races suggest that introgressive hybridization has occurred between them, allowing for the occupation of intermediate habitats.

Leaf morphophysiology of a Neotropical mistletoe is shaped by seasonal patterns of host leaf phenology

“…To cope readily with these potential metabolic differences in a diverse assemblage of host species, generalist mistletoes are expected to show rapid metabolic adaptation rates and a high degree of phenotypic plasticity that should be reflected in their morphology and physiology. For example, different populations of the same species of mistletoe can display variations in morphology, such as differences in internode length, fruit size and fruit pigmentation (Glazner et al 1988;May 1972). A high variation of leaf morphology and architecture within mistletoe species in relation to different host species and host populations has also been documented (Atsatt 1970;Herrera 1988;Medel et al 1995).…”

“…A high variation of leaf morphology and architecture within mistletoe species in relation to different host species and host populations has also been documented (Atsatt 1970;Herrera 1988;Medel et al 1995). Physiological specialization has also been reported, such as the large amount of aluminium (Al) in leaves of mistletoes parasitizing Al-accumulator hosts in acidic soils (Lüttge et al 1998;Scalon et al 2013) and differences in freeze tolerance and flavonoid content between two populations of the same mistletoe species in distinct locations (May 1972).…”