Viscaceae Batsch

Scientific Description

Common name. Christmas Mistletoe Family.

Habit and leaf form. Chlorophyllous but parasitic shrubs. ‘Normal’ plants, or switch-plants; sometimes with the principal photosynthesizing function transferred to stems. Leaves well developed, or much reduced. Plants rootless (in the normal sense — with haustoria); partially parasitic. On aerial parts of the host. 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. Leaves without stipules. Stem anatomy. Secondary thickening developing from a conventional cambial ring.

Reproductive type, pollination. Fertile flowers functionally male and functionally female, or functionally male, or functionally female, or hermaphrodite, functionally male, and functionally female. Unisexual flowers present. Plants monoecious, or dioecious, or polygamomonoecious. Anemophilous, or entomophilous.

Inflorescence and flower features. Flowers solitary to aggregated in ‘inflorescences’; in cymes, or in racemes, or in spikes. The terminal inflorescence unit cymose. Inflorescences terminal, or axillary; (1-)3-flowered dichasia in spikes or branched inflorescences. Flowers bracteate; minute to small; regular; (2–)4 merous; cyclic. Perianth sepaline, or petaline, or vestigial (often represented by mere bumps or teeth on the ovary rim); (2–)3, or 4; 1 -whorled; free, or joined; persistent, or deciduous. Calyx (if P so interpreted) (2–)3–4 (females often 3, males 4); 1 -whorled; polysepalous, or gamosepalous; entire, or lobed; when not entire, lobulate, or blunt-lobed, or toothed; valvate, or open in bud; regular; persistent, or not persistent. Fertile stamens present, or absent (females). Androecium (2–)4. Androecial members free of the perianth, or adnate (to the perianth); all equal; free of one another, or coherent (via the anthers); 1 -whorled. Androecium exclusively of fertile stamens. Stamens (2–)4; isomerous with the perianth; oppositisepalous; filantherous, or with sessile anthers. Anthers separate from one another, or cohering; dehiscing via pores, or dehiscing via short slits, or dehiscing via longitudinal slits, or dehiscing transversely; introrse; unilocular to 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, or stylate. Styles 1; apical. Placentation basal (i.e. 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 (sometimes), or passively dehiscent; 1(–2) seeded. Seeds endospermic; without a testa. Embryo weakly differentiated. Cotyledons 2. Embryo chlorophyllous (2/2).

Physiology, biochemistry. Aluminium accumulation not found.

Geography, cytology, number of species. World distribution: cosmopolitan, especially tropical and warm regions. X = 10–14 (polyploidy rare). 450 species.

Economic uses, etc. Viscum album and Phoradendron flavescens are the Yuletide mistletoes.