In the absence of the green aerial portions of the mistletoe plant, how ever, the root system of the parasite can utilize host nutrients and remain alive within an infected branch for many years. Because male and female flowers are so similar in appearance it is difficult to tell the sex of the plant unless fruit are present. Unopened male flowers on an infloresence of P. tomentosum ssp. Mature female flowers on an infloresence of P. villosum ssp. A berry usually holds a single seed surrounded by a sticky pulp.
Birds digest the pulp of the berry and excrete the living seed.
By this means seeds are often deposited on susceptible trees. A viscous coating and hair-like threads on the outer surface of the seeds attach excreted seeds firmly to tree branches. Upon germinating, the growing radicle becomes tightly pressed to the branch surface. Young or small trees are seldom infected by mistletoe. In nearly all cases, initial infection occurs on larger or older trees because birds prefer to perch in the tops of taller trees.