Illinois

• Adams 17001
  1,183 taxa Open ↗
• Alexander 17003
  1,220 taxa Open ↗
• Bond 17005
  682 taxa Open ↗
• Boone 17007
  1,163 taxa Open ↗
• Brown 17009
  836 taxa Open ↗
• Bureau 17011
  652 taxa Open ↗
• Calhoun 17013
  1,017 taxa Open ↗
• Carroll 17015
  931 taxa Open ↗
• Cass 17017
  1,389 taxa Open ↗
• Champaign 17019
  1,420 taxa Open ↗

Showing 2,351–2,400 of 3,775.

• 
  Oligoneuron riddellii (Frank ex Riddell) Rydb. Native OLRI2

  Riddell's goldenrod · Asteraceae 27 counties
• 
  Oligoneuron rigidum (L.) Small Native OLRI

  stiff goldenrod · Asteraceae 86 counties
• 
  Oligoneuron rigidum (L.) Small var. rigidum Native OLRIR

  stiff goldenrod · Asteraceae 86 counties
• ⚘
  Oligoneuron ×lutescens (Lindl. ex DC.) G.L. Nesom [album × rigidum] Native OLLU

  goldenrod · Asteraceae 1 county
• 
  Onobrychis viciifolia Scop. Introduced ONVI

  sainfoin · Fabaceae 1 county
• 
  Onoclea sensibilis L. Native ONSE

  sensitive fern · Dryopteridaceae 89 counties
• 
  Ononis spinosa L. Introduced ONSP

  spiny restharrow · Fabaceae 1 county
• 
  Onopordum acanthium L. Introduced ONAC

  Scotch cottonthistle · Asteraceae 2 counties
• 
  Onosmodium bejariense DC. ex A. DC. Native ONBE

  soft-hair marbleseed · Boraginaceae 37 counties
• 
  Onosmodium bejariense DC. ex A. DC. var. bejariense Native ONBEB

  soft-hair marbleseed · Boraginaceae 37 counties
• 
  Onosmodium bejariense DC. ex A. DC. var. hispidissimum (Mack.) B.L. Turner Native ONBEH

  softhair marbleseed · Boraginaceae 26 counties
• 
  Onosmodium bejariense DC. ex A. DC. var. occidentale (Mack.) B.L. Turner Native ONBEO

  western marbleseed · Boraginaceae 23 counties
• 
  Ophioglossum engelmannii Prantl Native OPEN

  limestone adderstongue · Ophioglossaceae 9 counties
• 
  Ophioglossum pusillum Raf. Native OPPU3

  northern adderstongue · Ophioglossaceae 36 counties
• 
  Ophioglossum vulgatum L. Native OPVU

  southern adderstongue · Ophioglossaceae 4 counties
• 
  Opuntia fragilis (Nutt.) Haw. Native OPFR

  brittle pricklypear · Cactaceae 1 county
• 
  Opuntia humifusa (Raf.) Raf. Native OPHU

  devil's-tongue · Cactaceae 47 counties
• 
  Opuntia macrorhiza Engelm. Native OPMA2

  twistspine pricklypear · Cactaceae 4 counties
• 
  Opuntia macrorhiza Engelm. var. macrorhiza Native OPMAM3

  twistspine pricklypear · Cactaceae 4 counties
• 
  Orbexilum onobrychis (Nutt.) Rydb. Native ORON

  French-grass · Fabaceae 51 counties
• 
  Orbexilum pedunculatum (Mill.) Rydb. Native ORPE

  Sampson's snakeroot · Fabaceae 32 counties
• 
  Orbexilum pedunculatum (Mill.) Rydb. var. pedunculatum Native ORPEP2

  Sampson's snakeroot · Fabaceae 32 counties
• 
  Ornithogalum nutans L. Introduced ORNU

  drooping star of Bethlehem · Liliaceae 1 county
• 
  Ornithogalum umbellatum L. Introduced ORUM

  star of Bethlehem · Liliaceae 63 counties
• 
  Orobanche fasciculata Nutt. Native ORFA

  clustered broomrape · Orobanchaceae 9 counties
• 
  Orobanche ludoviciana Nutt. Native ORLU

  Louisiana broomrape · Orobanchaceae 9 counties
• 
  Orobanche ludoviciana Nutt. ssp. ludoviciana Native ORLUL2

  Louisiana broomrape · Orobanchaceae 9 counties
• 
  Orobanche ramosa L. Introduced ORRA

  hemp broomrape · Orobanchaceae 1 county
• 
  Orobanche riparia L.T. Collins Native ORRI

  River Broom-Rape · Orobanchaceae 5 counties
• 
  Orobanche uniflora L. Native ORUN

  oneflowered broomrape · Orobanchaceae 42 counties
• 
  Orthilia secunda (L.) House Native ORSE

  sidebells wintergreen · Pyrolaceae 3 counties
• 
  Oryzopsis asperifolia Michx. Native ORAS

  roughleaf ricegrass · Poaceae 1 county
• 
  Osmorhiza claytonii (Michx.) C.B. Clarke Native OSCL

  Clayton's sweetroot · Apiaceae 76 counties
• 
  Osmorhiza longistylis (Torr.) DC. Native OSLO

  longstyle sweetroot · Apiaceae 80 counties
• 
  Osmunda cinnamomea L. Native OSCI

  cinnamon fern · Osmundaceae 28 counties
• 
  Osmunda cinnamomea L. var. cinnamomea Native OSCIC

  cinnamon fern · Osmundaceae 28 counties
• 
  Osmunda claytoniana L. Native OSCL2

  interrupted fern · Osmundaceae 43 counties
• 
  Osmunda regalis L. Native OSRE

  royal fern · Osmundaceae 33 counties
• 
  Osmunda regalis L. var. spectabilis (Willd.) A. Gray Native OSRES

  royal fern · Osmundaceae 33 counties
• 
  Ostrya virginiana (Mill.) K. Koch Native OSVI

  hophornbeam · Betulaceae 102 counties
• 
  Oxalis corniculata L. Native OXCO

  creeping woodsorrel · Oxalidaceae 9 counties
• 
  Oxalis dillenii Jacq. Native OXDI2

  slender yellow woodsorrel · Oxalidaceae 102 counties
• 
  Oxalis illinoensis Schwegm. Native OXIL

  Illinois woodsorrel · Oxalidaceae 2 counties
• 
  Oxalis stricta L. Native OXST

  common yellow oxalis · Oxalidaceae 102 counties
• 
  Oxalis violacea L. Native OXVI

  violet woodsorrel · Oxalidaceae 102 counties
• 
  Oxydendrum arboreum (L.) DC. Native OXAR

  sourwood · Ericaceae 1 county
• 
  Oxypolis rigidior (L.) Raf. Native OXRI

  stiff cowbane · Apiaceae 43 counties
• 
  Packera aurea (L.) Á. Löve & D. Löve Native PAAU3

  golden ragwort · Asteraceae 52 counties
• 
  Packera glabella (Poir.) C. Jeffrey Native PAGL17

  butterweed · Asteraceae 51 counties
• 
  Packera obovata (Muhl. ex Willd.) W.A. Weber & Á. Löve Native PAOB6

  roundleaf ragwort · Asteraceae 14 counties