| Bidens pilosa, Bidens tripartita, Bidens alba, Bidens frondosa, Bidens ferulifolia|
Bidens is a genus of flowering plants in the aster family, Asteraceae. The common names beggarticks, black jack, burr marigolds, cobbler's pegs, Spanish needles, stickseeds, tickseeds and tickseed sunflowers refer to the fruits of the plants, most of which are bristly and barbed, with two sharp pappi at the end. The generic name refers to the same character; Bidens comes from the Latin bis ("two") and dens ("tooth").
The plants are zoochorous; their seeds will stick to clothing, fur or feathers, and be carried to new habitat. This has enabled them to colonize a wide range, including many oceanic islands. Some of these species occur only in a very restricted range and several are now threatened with extinction, notably in the Hawaiian Islands. Due to the absence of native mammals on these islands, some of the oceanic island taxa have reduced burrs, evolving features that seem to aid in dispersal by the wind instead.
Bidens is distributed throughout the tropical and warm temperate regions of the world. Most species occur in the Americas, Africa, and Polynesia, and there are some in Europe and Asia. Bidens is closely related to the American genus Coreopsis, and the genera are sometimes difficult to tell apart; in addition, neither is monophyletic.
On the Hawaiian Islands, Bidens are called kokoʻolau or koʻokoʻolau.
Nodding beggarticks (B. cernua) and hairy beggarticks (B. pilosa) are useful as honey plants. Several Bidens species are used as food by the caterpillars of certain Lepidoptera, such as the noctuid moth Hypercompe hambletoni and the brush-footed butterfly Vanessa cardui, the Painted Lady. The Bidens mottle virus, a plant pathogen, was first isolated from B. pilosa, and it infects many other Asteraceae and plants of other families.
The taxonomy of Bidens has been described as "chaotic", and it is not clear how many taxa are included in its bounds. There are probably at least 150 to 250 species, and some estimates fall around 230.
Species include:Bidens alba (L.) DC. – romerillo
Bidens amplectens Sherff – Waiʻanae kokoʻolau
Bidens amplissima Greene – Vancouver Island beggarticks
Bidens aristosa (Michx.) Britt. – bearded beggarticks, long-bracted beggarticks, tickseed sunflower, western tickseed
Bidens asymmetrica (Levl.) Sherff – Koʻolau kokoʻolau, Ko'olau Range beggarticks
Bidens aurea (Ait.) Sherff – Arizona beggarticks
Bidens beckii – Beck's water-marigold, Henderson's water-marigold, Oregon water-marigold
Bidens bidentoides (Nutt.) Britt. – Delmarva beggarticks
Bidens bigelovii A.Gray – Bigelow's beggarticks
Bidens bipinnata L. – Spanish needles, hemlock beggarticks, gui zheng cao (Chinese: 鬼針草)
Bidens campylotheca Sch.Bip.– viper beggarticks
Bidens cernua L. (syn. B. glaucescens Greene) – nodding beggarticks, nodding bur-marigold
Bidens cervicata Sherff – Kauaʻi beggarticks
Bidens chippii (M.B.Moss) Mesfin
Bidens conjuncta Sherff – bog beggarticks
Bidens connata Muhl. ex Willd. – purplestem beggarticks
Bidens coronata (L.) Britt. – crowned beggarticks
Bidens cosmoides (A.Gray) Sherff – cosmosflower beggarticks, poʻola nui
Bidens cynapiifolia Kunth – West Indian beggarticks, alfilerillo
Bidens discoidea (Torr. & A.Gray) Britt. – discoid beggarticks, small beggarticks, swamp beggarticks, few-bracted beggarticks
Bidens eatonii Fern. – Eaton's beggarticks, bident d'Eaton
Bidens ferulifolia (Jacq.) DC. – Apache beggarticks, fern-leaved beggarticks
Bidens forbesii Sherff – coastal bluff beggarticks
Bidens frondosa L. – devil's beggarticks, devil's pitchfork, devil's bootjack, pitchfork weed, common beggarticks, sticktights. Pitchfork weed (B. frondosa) is considered to be a weed in New Zealand.
Bidens gardneri Baker – ridge beggarticks
Bidens hawaiensis A.Gray – Hawaiʻi beggarticks
Bidens henryi Sherff
Bidens heterodoxa (Fern.) Fern. & H.St.John – Connecticut beggarticks, bident différent
Bidens heterosperma Gray – Rocky Mountain beggarticks
Bidens hillebrandiana (Drake) O.Deg. – seacliff beggarticks
Bidens hyperborea Greene – estuary beggarticks, coastal beggarticks, northern estuarine beggarticks, seacliff beggarticks
Bidens laevis (L.) B.S.P. – smooth beggarticks, smooth bur-marigold, larger bur-marigold. Smooth beggarticks (B. laevis) is a common fall flower in the southeastern United States.
Bidens lemmonii Gray – Lemmon's beggarticks
Bidens leptocephala Sherff – few-flowered beggarticks
Bidens macrocarpa (Gray) Sherff – large-fruited beggarticks
Bidens mannii T.G.J.Rayner
Bidens mauiensis (Gray) Sherff – Maui beggarticks
Bidens menziesii (Gray) Sherff – Mauna Loa beggarticks
Bidens meyeri V.A.Funk & K.R.Wood
Bidens micrantha Gaud. – grassland beggarticks
B. micrantha ssp. kalealaha Nagata & Ganders – Kalealaha beggarticks
Bidens mitis (Michx.) Sherff – small-fruited beggarticks
Bidens molokaiensis (Hillebr.) Sherff – Molokaʻi beggarticks, wedge beggarticks
Bidens × multiceps Fassett
Bidens pilosa S.F.Blake – hairy beggarticks
Bidens polylepis S.F.Blake
Bidens populifolia Sherff – Oʻahu beggarticks
Bidens reptans (L.) G.Don – manzanilla trepador
Bidens sandvicensis Less. – shrubland beggarticks
Bidens schimperi Sch.Bip.
Bidens simplicifolia C.H.Wright
Bidens squarrosa Kunth
Bidens subalternans DC.
Bidens tenuisecta A.Gray – slim-lobed beggarticks
Bidens torta Sherff – corkscrew beggarticks
Bidens trichosperma (Michx.) Britton – crowned beggarticks
Bidens tripartita L. (syn. B. acuta, B. comosa) – three-lobed beggarticks, three-part beggarticks, leafy-bracted beggarticks, trifid bur-marigold
Bidens triplinervia Kunth
B. triplinervia var. macrantha (Wedd.) Sherff
Bidens valida Sherff – Mt. Kahili beggarticks
Bidens vulgata Greene – big devil's beggarticks, tall beggarticks, tall bur-marigold, western sticktight
Bidens wiebkei Sherff – Wiebke's beggarticks
Cosmos atrosanguineus (Hook.) Voss (as B. atrosanguinea (Hook.) Ortgies ex Regel)
Cosmos bipinnatus Cav. (as B. formosa (Bonato) Sch.Bip.)
Melanthera nivea (L.) Small (as B. nivea L.)
Salmea scandens (L.) DC. (as B. scandens L.)
Thelesperma megapotamicum (Spreng.) Kuntze (as B. megapotamica Spreng.)
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