Phenology of Psittacanthus palmeri (Loranthaceae), a deciduous mistletoe, and its host Bursera fagaroides

Abstract

Deciduousness is a common trait among plants inhabiting semi-arid regions; however, this foliar habit is rare in mistletoes and has not been documented in tropical species. In Central Mexico, Psittacanthus palmeri parasitizes Bursera fagaroides trees. Both species share similar characteristics, such as shedding their leaves during the dry season and having notably similar fruit morphology. To document the deciduous habit of P. palmeri and investigate whether its phenophases align with those of B. fagaroides, we evaluated the phenological changes of both species over the course of one year. Additionally, we compared the mean fruit size of both species to evaluate their morphological similarity. Both species exhibit a leafless phase during the dry season, although B. fagaroides’s leafless period is more extended. Their flowering phenophases differ: B. fagaroides flowers during the dry season with an intermediate duration and mid-synchronic timing, while P. palmeri flowers during the rainy season with an extended duration and non-synchronous timing. The fruiting phase for Bursera is extended, synchronous, and even forming aerial seed bank. In contrast, the fruiting phase of P. palmeri is extended (but not more than six months), occurs during autumn-winter, and is non-synchronous. The fruits of both species are very similar in size (t = 1.086, d.f. = 118, p = 0.279) and color, suggesting they may share disperser birds, potentially enhancing seed dispersal for both species. However, this hypothesis requires further research. P. palmeri is a poorly studied mistletoe, and its unique features, such as deciduous habit, inconspicuous nature and a possible mimicry of the host, opens new opportunities of research.