Viscum L.

Scientific Description

Family Viscaceae.

Habit and leaf form. Chlorophyllous but parasitic shrubs. ‘Normal’ plants, or switch-plants; with the principal photosynthesizing function transferred to stems. Leaves well developed, or much reduced (to small scales), or absent (apparently). Plants rootless (in the normal sense — with haustoria); partially parasitic. On aerial parts of the host. Young stems cylindrical (internodes, or successively flattened alternately). Stem internodes solid. Stem growth conspicuously sympodial (often pseudodichotomous), or not conspicuously sympodial. Mesophytic, or xerophytic. Leaves opposite; ‘herbaceous’, or leathery, or membranous; simple. Leaf blades entire; one-veined, or parallel-veined (curvinerved). Leaves without stipules. Leaf blade margins entire. Leaf anatomy. Hairs absent. Extra-floral nectaries absent.

Reproductive type, pollination. Fertile flowers functionally male and functionally female. Unisexual flowers present. Plants monoecious (in Australian species). Female flowers without staminodes. Male flowers without pistillodes. Anemophilous, or entomophilous.

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in cymes (of 1–5 flowers), or in fascicles (or clusters at nodes). The terminal inflorescence unit cymose. Inflorescences axillary (in Australian species); cyme sessile or pedunculate, either male or female flowers central in cyme. Flowers bracteate (2, boat-shaped, subtending each inflorescence); ebracteolate; minute to small; regular; cyclic. Perianth sepaline; 2–4; 1 -whorled; deciduous. Calyx present; if P so interpreted, 2–4; polysepalous, or gamosepalous; valvate; regular; not persistent. Sepals triangular. Calyx lobes triangular. Fertile stamens present, or absent (females). Androecial members definite in number. Androecium 2–4. Androecial members adnate (to the perianth); all equal (anthers); free of one another; 1 -whorled. Androecium exclusively of fertile stamens. Stamens 2–4; all more or less similar in shape (anthers); isomerous with the perianth; oppositisepalous; with sessile anthers. Anthers separate from one another (free from each other but adnate to the perianth); non-versatile; dehiscing via pores (terminal); introrse; many locular; bisporangiate, or tetrasporangiate. Fertile gynoecium present, or absent (males). Gynoecium 3 carpelled, or 4 carpelled. The pistil 1 celled. Carpels isomerous with the perianth, or reduced in number relative to the perianth. Gynoecium syncarpous; eu-syncarpous; inferior. Ovary unilocular; 1 locular. Gynoecium non-stylate. Styles 1; apical. Stigmas 1. Placentation basal (with a short placental column). Ovules not differentiated; in the single cavity 2; sessile; ascending; orthotropous.

Fruit and seed features. Fruit fleshy; indehiscent; a berry (with viscous tissue within); elastically dehiscent, or passively dehiscent; 1(–2) seeded. Seeds endospermic; without a testa. Embryo weakly differentiated. Cotyledons 2.

Economic uses, etc. Viscum album is one of the Yuletide mistletoes.

Etymology. From the Latin for "mistletoe", V. album; bird-lime, which was made from the berries; also applied by Pliny to Loranthus europaeus.