{{Short description|Genus of flowering plants}} {{Automatic taxobox |image = Acaena novae-zelandiae1.jpg |image_caption = ''Acaena novae-zelandiae'' foliage and various fruiting stages |display_parents = 3 |taxon = Acaena |authority = Mutis ex L.<ref name=GRIN>{{GRIN genus | name = ''Acaena'' | id = 27 | accessdate = 30 March 2020}}</ref> |subdivision_ranks = Species |subdivision = See text |synonyms = *''Ancistrum'' {{Au|J.R.Forst. & G.Forst.}} |synonyms_ref = <ref name=GRIN/> }}
'''''Acaena''''' is a genus of about 60 species of mainly evergreen, creeping herbaceous perennial plants and subshrubs in the family Rosaceae, native mainly to the Southern Hemisphere, notably New Zealand, Australia and South America, but with a few species extending into the Northern Hemisphere, north to Hawaii (''A. exigua'') and California (''A. pinnatifida'').<ref>{{cite book|title=RHS A-Z encyclopedia of garden plants|year=2008|publisher=Dorling Kindersley|location=United Kingdom|isbn=1405332964|page=1136}}</ref>
The leaves are alternate, {{convert|4|-|15|cm|in}} long, and pinnate or nearly so, with 7–21 leaflets. The flowers are produced in a tight globose [inflorescence] {{convert|1|-|2|cm|in}} in diameter, with no petals. The fruit is also a dense ball of many seeds; in many (but not all) species the seeds bear a barbed arrowhead point, the seedhead forming a burr which attaches itself to animal fur or feathers for dispersal.
Several ''Acaena'' species in New Zealand are known by the common name '''bidibid'''. The word is written variously ''bidi-bidi'', ''biddy-biddy'', ''biddi-biddi'', ''biddi-bid'' and a number of other variations. These names are the English rendition of the original Māori name of ''piripiri''.<ref>Orsman, H. W. (1999). ''The Dictionary of New Zealand English''. Auckland: Oxford University Press.</ref> The plant is also called the New Zealand burr. The species ''Acaena microphylla'' has gained the Royal Horticultural Society's Award of Garden Merit.<ref>[http://apps.rhs.org.uk/plantselector/plant?plantid=13 RHS Plant Selector Acaena microphylla AGM / RHS Gardening<!-- Bot generated title -->]{{Dead link|date=June 2025 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>
== Etymology == The generic name ''Acaena'' is derived from the Greek "akaina" (thorn), referring to the spiny hypanthium.<ref>{{cite web|website= E-Flora (Flora of North America)|title= Rosaceae 26. Acaena|author= Bryony Macmillan|url= http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=100063|accessdate= 2015-12-03}}</ref>
==Species== {{As of|2020}}, Plants of the World Online accepted the following species:<ref name=POWO>{{cite web | title = ''Acaena'' | work = Plants of the World Online | publisher = Royal Botanic Gardens, Kew | url = https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:30001386-2 | accessdate = 30 March 2020}}</ref> {{Div col}} *''Acaena agnipila'' {{Au|Gand.}} *''Acaena alpina'' {{Au|Poepp. ex Walp.}} *''Acaena anserinifolia'' {{Au|(J.R.Forst. & G.Forst.) J.B.Armstr.}} *''Acaena antarctica'' {{Au|Hook.f.}} *''Acaena argentea'' {{Au|Ruiz & Pav.}} *''Acaena boliviana'' {{Au|Gand.}} *''Acaena buchananii'' {{Au|Hook.f.}} *''Acaena caesiiglauca'' {{Au|(Bitter) Bergmans}} – glaucous pirri-pirri-bur *''Acaena caespitosa'' {{Au|Gillies ex Hook. & Arn.}} *''Acaena confertissima'' {{Au|Bitter}} *''Acaena cylindristachya'' {{Au|Ruiz & Pav.}} *''Acaena dumicola'' {{Au|B.H.Macmill.}} (South Island of New Zealand) *''Acaena echinata'' {{Au|Nees}} – sheep's burr *''Acaena elongata'' {{Au|L.}} *''Acaena emittens'' {{Au|B.H.Macmill.}} (North Island of New Zealand) *''Acaena eupatoria'' {{Au|Cham. & Schltdl.}} *''Acaena exigua'' {{Au|A.Gray}} – ''liliwai'' (Hawai{{okina}}i) *''Acaena fissistipula'' {{Au|Bitter}} *''Acaena fuscescens'' {{Au|Bitter}} *''Acaena glabra'' {{Au|Buchanan}} *''Acaena hirsutula'' {{Au|Bitter}} *''Acaena inermis'' {{Au|Hook.f.}} *''Acaena integerrima'' {{Au|Gillies ex Hook. & Arn.}} *''Acaena juvenca'' {{Au|B.H.Macmill.}} (New Zealand) *''Acaena latebrosa'' {{Au|W.T.Aiton}} *''Acaena leptacantha'' {{Au|Phil.}} *''Acaena longiscapa'' {{Au|Bitter}} *''Acaena lucida'' {{Au|(Aiton) Vahl}} *''Acaena macrocephala'' {{Au|Poepp.}} *''Acaena magellanica'' {{Au|(Lam.) Vahl}} – greater burnet *''Acaena masafuerana'' {{Au|Bitter}} *''Acaena microphylla'' {{Au|Hook.f.}} – New Zealand-bur *''Acaena minor'' {{Au|(Hook.f.) Allan}} *''Acaena montana'' {{Au|Hook.f.}} *''Acaena myriophylla'' {{Au|Lindl.}} *''Acaena novae-zelandiae'' {{Au|Kirk}} – red bidibid (New Zealand) *''Acaena ovalifolia'' {{Au|(Vahl) Ruiz & Pav.}} *''Acaena ovina'' {{Au|A.Cunn.}} *''Acaena pallida'' {{Au|(Kirk) Allan}} – sand bidibid *''Acaena patagonica'' {{Au|A.E.Martic.}} *''Acaena pinnatifida'' {{Au|Ruiz & Pav.}} – Argentinian biddy-biddy *''Acaena platyacantha'' {{Au|Speg.}} *''Acaena poeppigiana'' {{Au|Gay}} *''Acaena profundeincisa'' {{Au|(Bitter) B.H.Macmill.}} *''Acaena pumila'' {{Au|Vahl}} *''Acaena rorida'' {{Au|B.H.Macmill.}} (North Island) *''Acaena saccaticupula'' {{Au|Bitter}} *''Acaena sarmentosa'' {{Au|(Thouars) Carmich.}} *''Acaena sericea'' {{Au|J.Jacq.}} *''Acaena splendens'' {{Au|Hook. & Arn.}} *''Acaena stangii'' {{Au|Christoph.}} *''Acaena stricta'' {{Au|Griseb.}} *''Acaena subincisa'' {{Au|Wedd.}} *''Acaena tenera'' {{Au|Albov}} – lesser burnet *''Acaena tesca'' {{Au|B.H.Macmill.}} (South Island) *''Acaena torilicarpa'' {{Au|Bitter}} *''Acaena trifida'' {{Au|Ruiz & Pav.}} {{Div col end}}
==Invasive species== Some species have been introduced accidentally to other areas, attached to sheep's wool, and have become invasive species. ''Acaena novae-zelandiae'', one of the bidibids from New Zealand, is the most commonly encountered species in the United Kingdom, where it is often abundant on coastal sand dunes, crowding out native vegetation and creating an often painful nuisance with the barbed burrs. In California, ''A. pallida'', ''A. novae-zelandiae'' and ''A. anserinifolia'' are considered serious weeds.<ref>[https://archive.today/20130616101927/http://www.cdfa.ca.gov/plant/ipc/weedinfo/winfo_list-pestrating.htm "Weeds Sorted by Pest Rating"], CFDA.ca.gov</ref>
==References== {{Reflist}}
==External links== {{Commons category}} *[http://ucjeps.berkeley.edu/cgi-bin/get_JM_treatment.pl?6677,6678 Jepson Manual Treatment] *[https://plants.usda.gov/java/profile?symbol=ACAEN USDA Plants Profile] *[https://web.archive.org/web/20080408043341/http://www.landcareresearch.co.nz/ Landcare Research New Zealand]
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Category:Acaena Category:Pantropical flora Category:Rosaceae genera