Thesium L.

Annual or perennial herbs or rarely shrubs, often root parasites on grasses, decumbent or erect, slender with woody base, evergreen, often hemi-parasites on roots. Leaves alternate, usually sessile, linear or scale-like, 1 – 3-nerved; lateral nerves indistinct. Inflorescences apparently terminal, dichotomous racemes, often paniculate, rarely cymose or axillary, solitary. Flowers: bisexual, minute, white or yellowish green, with a slender pedicel bearing a linear leaflike bract and 2 bracteoles; perianth campanulate or infundibuliform; perianth-tube cylindrical, tubular or funnel-shaped, adnate to ovary at basal part; perianth-limb divided above into 5 or rarely 4 linear-acute valvate lobes; each lobe hooded at apex; stamens 5 (or 4), inserted at the base of the perianth-lobes; filaments inserted; disc inconspicuous, connate to the base of perianth-tube; ovary inferior, sessile or slightly stalked; ovules 2 or 3, pendulous from a basal free, often flexuous or crumpled column; style short or long; stigma capitate or 3-lobulate. Fruit a small nut, often weakly ribbed, bearing remnants of perianth; exocarp dry, membranous, rarely fleshy; endocarp bony, slightly ridged; endosperm fleshy; embryo terete, straight or oblique; cotyledons small; radicle as long as or longer than the cotyledons.

Temperate and subtropical regions of Old World, many in Africa, ca 325 species; 5 species in India.

KEY TO THE SPECIES

1 a. Flowers sessile

2

b. Flowers pedicellate

3

2 a. Plants non-parasitic; taproot system distinct, not stoloniferous

4. Thesium unicaule

b. Plants parasitic; taproot system indistinct, stoloniferous

5. Thesium wightianum

3 a. Leaves 1 – 2 cm long; bracts 6 – 12 mm long; perianth funnel-shaped; perianth lobes narrowly oblong, acute, distinctly recurved

1. Thesium emodi

b. Leaves 2.5 – 3.5 cm long; bracts 3 – 6 mm long; perianth bell-shaped; perianth lobes broadly oblong to ovate, obtuse, slightly recurved

4

4 a. Plants with taproot, not stoloniferous; peduncles 3 – 12 mm long; bracts linear to linear- lanceolate, 1-nerved; bracteoles shorter than bracts and flower in length; flowers 2.5 – 3.5 mm long; pedicels 1 – 3 mm in flower, up to 12 mm long in fruit

2. Thesium himalense

b. Plants without tap root, stoloniferous; peduncles 10 – 20 mm long; bracts leaf-like, 1 – 3- nerved; bracteoles 4 – 7 mm long, equalling or exceeding the flower in length;flowers 3.5 – 5 mm long; pedicels 7 – 10 mm long in flower, up to 20 mm long in fruit

3. Thesium hookeri

List of Lower Taxa