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FOC | Family List | FOC Vol. 5 | Santalaceae

5. Thesium Linnaeus, Sp. Pl. 1: 207. 1753.

百蕊草属 bai rui cao shu

Herbs perennial or annual, slender, sometimes subshrubs, often root hemiparasites of grasses, ± evergreen. Stems green. Leaves alternate, usually sessile, usually linear or, sometimes, scale-like, 1-3-veined, lateral veins not apparent. Inflorescences apparently terminal, usually racemelike, often paniculate, less often cymose (or axillary and 1-flowered); bracts and bracteoles leaflike, sometimes partly adnate to pedicels; bracteoles 1 or 2 and opposed, rarely 4, sometimes absent. Flowers bisexual, white or yellowish green; perianth tube connate to ovary, limb campanulate, cylindric, funnelform, or tubular, usually deeply (4 or)5-lobed, lobes valvate, usually with a tuft of hair behind each stamen. Stamens (4 or)5, usually on the base of lobes; filaments not exserted; anthers ovoid or ellipsoid, cells parallel, dehiscence longitudinal. Disk superior, inconspicuous or connate to base of perianth tube. Ovary inferior, stalked or sessile; ovules 2 or 3, pendulous from apex of placenta, usually flexuous or corrugate. Style long or short; stigma capitate or inconspicuously 3-lobed. Fruit a small nut, with persistent perianth at apex, exocarp dry, membranous [rarely fleshy], endocarp bony or slightly rigid, usually ridged; embryo in the middle of fleshy endosperm, erect or slightly curved, usually oblique, terete, radicle as long as or slightly longer than cotyledons.

About 245 species: widely distributed in temperate regions of the Old World, especially numerous in S Africa, a few species in tropical and temperate South America; 16 species (nine endemic) in China.

The inflorescence of Thesium has been interpreted in different ways. In the majority of species it is axillary and 1-flowered with a pair of bracts at the apex of the peduncle, which is often fused to the subtending leaf, and with the pedicel proper very short to almost absent. In practice, botanists have often assumed that the inflorescence is a raceme with the peduncles as pedicels and bracts as bracteoles, and for convenience that interpretation has been maintained here.

Thesium chanetii H. Léveillé and T. glabrum Schindler are both Diarthron linifolium Turczaninow (Thymelaeaceae). A record of Thesium australe R. Brown (Prodr. 353. 1810) from Hainan is probably based on a misidentification of the very similar T. chinense Turczaninow.

1 Leaves scale-like; inflorescence cymose; bracts and bracteoles very small and scale-like.   16 T. psilotoides
+ Leaves linear to oblong-linear, broadly lanceolate, or oblong (scale-like leaves sometimes present at base of stem); inflorescence racemelike; bracts linear, leaflike.   (2)
2 (1) Pedicels 25-40 mm; bract inserted at base of pedicel.   14 T. remotebracteatum
+ Pedicels to 25 mm; bract often inserted at least partway along pedicel.   (3)
3 (2) Fruit with reticulate veins; ovary sessile.   (4)
+ Fruit with longitudinal veins, veins sometimes forked but not reticulate; ovary stalked.   (5)
4 (3) Plants robust; stems erect or ascending; flowers 4(or 5)-merous; persistent perianth hypocrateriform, longer than fruit.   5 T. cathaicum
+ Plants slender; stems ascending; flowers 5-merous; persistent perianth subglobose, shorter than fruit.   6 T. chinense
5 (3) Stems usually procumbent; branches and leaves sparse.   (6)
+ Stems erect or ascending, rarely procumbent; branches and leaves often dense.   (9)
6 (5) Perianth subcampanulate; leaves 2.5-3 cm.   1 T. himalense
+ Perianth funnelform to tubular; leaves 1-2.5 cm.   (7)
7 (6) Leaves with minutely denticulate margins, ca. 2.5 cm; flowers funnelform, sometimes in clusters of 2 or 3.   15 T. brevibracteatum
+ Leaves with entire margins, 1-2 cm; flowers narrowly funnelform to tubular, always solitary.   (8)
8 (7) Flowers narrowly funnelform to subtubular; leaves oblong, ca. 1 cm.   2 T. emodi
+ Flowers tubular; leaves linear, ca. 2 cm.   3 T. tongolicum
9 (5) Flowers in proximal inflorescences usually in groups of 2 or 3; racemes usually branched into panicles.   4 T. ramosoides
+ Flower always 1 per axil; racemes usually with few or no branches.   (10)
10 (9) Fruit 5-6 mm in diam., subglobose; persistent perianth slightly longer than fruit; flowers broadly campanulate.   10 T. jarmilae
+ Fruit 2-4.5 mm in diam., usually ellipsoid; persistent perianth shorter or longer than fruit; flowers broadly funnelform, tubular, or campanulate.   (11)
11 (10) Bracts at base of pedicels; leaves 0.7-1.8 cm.   (12)
+ Bracts and bracteoles at top of pedicels; leaves lanceolate, linear, or oblong to oblong-linear, 3-5 cm.   (13)
12 (11) Flowers 6-10 mm; leaves linear, sometimes lanceolate, 0.7-1.7 cm.   11 T. longiflorum
+ Flowers 4-5 mm; leaves oblong-lanceolate, 1.5-1.8 cm.   13 T. orgadophilum
13 (11) Bracteoles much shorter than bracts; leaves lanceolate, apex acute, usually falcate.   7 T. arvense
+ Bracteoles slightly shorter than or as long as bracts; leaves lanceolate, linear, or oblong to oblong-linear, apex acuminate or obtuse.   (14)
14 (13) Fruit stalks reflexed when fruit mature; leaves usually 1-veined.   8 T. refractum
+ Fruit stalks not reflexed when fruit mature; leaves 3-veined.   (15)
15 (14) Stems ascending; perianth yellowish white, campanulate, 4-5 mm.   9 T. longifolium
+ Stems erect; perianth white, tubular, ca. 7 mm.   12 T. bomiense

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