Viscum

Shrubs [herbs], dioecious [monoecious]; parasitic on branches of woody angiosperms and gymnosperms, infections localized. Stems single or multiple; branching pseudodichotomous [percurrent]. Leaves well developed [scalelike]. Inflorescences axillary or terminal, dichasial cymes. Staminate flowers: petals (3–)4(–6), triangular, distinct; stamens (3–)4(–6); anthers multilocular, dehiscing by numerous pores; nectary absent. Pistillate flowers: petals (3–)4(–6), triangular, distinct; ovary 0-locular; style absent [short-conic]; stigma poorly differentiated [capitate]. Berries sessile in bracteal cup [pedicel present, not recurved], not explosively dehiscent, 1-colored, smooth [warty], scars of petal remnants at apex. Seeds mucilaginous when removed from fruit, endosperm slightly flattened, ovate to elliptic in broadest outline; embryo oriented transversely. x = 14.

Distribution

Introduced; Eurasia, Africa, Indian Ocean Islands, Australia.

Discussion

Species ca. 130 (1 in the flora).

Viscum is widely distributed in the Old World and is present in North America via purposeful introduction. The genus is most diverse in tropical and southern Africa, where various species form a decreasing aneuploid series (from × = 14) (D. Wiens 1975). Higher gametic chromosome numbers are the result of polyploidy, relatively uncommon in Viscaceae. Several species of dioecious Viscum show translocation heterozygosity that determines plant sexuality and sex ratios in populations (A. Aparicio 1993; Wiens and B. A. Barlow 1979).

Selected References

Bussing, A., ed. 2000. Mistletoe: The genus Viscum. Amsterdam.

Gill, L. S. 1935. Arceuthobium in the United States. Trans. Connecticut Acad. Arts 32: 111–245

Wiens, D. and B. A. Barlow. 1979. Translocation heterozygosity and the origin of dioecy in Viscum. Heredity 42: 201–222.

Lower Taxa

Viscum album