2006 (Map)  Obolaria virginica                       PENNYWORT
2007 (Map)  Ocimum basilicum                         BASIL
2008 (Map)  Oenothera biennis                        EVENING PRIMROSE
2009 (Map)  Oenothera biennis canescens              EVENING PRIMROSE
2010 (Map)  Oenothera fruticosa                      SHRUBBY SUNDROPS
2011 (Map)  Oenothera fruticosa glauca               FOUR-ANGLED SUNDROPS
2012 (Map)  Oenothera laciniata                      RAGGED EVENING PRIMROSE
2013 (Map)  Oenothera linifolia                      THREAD-LEAVED SUNDROPS
2014 (Map)  Oenothera macrocarpa                     MISSOURI PRIMROSE
2015 (Map)  Oenothera nuttallii                      WHITE EVENING PRIMROSE
2016 (Map)  Oenothera parviflora                     EVENING PRIMROSE
2017 (Map)  Oenothera perennis                       SMALL SUNDROPS
2018 (Map)  Oenothera pilosella                      PRAIRIE SUNDROPS
2019 (Map)  Oenothera rhombipetala                   SAND PRIMROSE
2020 (Map)  Oenothera speciosa                       SHOWY EVENING PRIMROSE
2021 (Map)  Oenothera triloba                        EVENING PRIMROSE
2022 (Map)  Onobrychis viciaefolia                   SAINFOIN
2023 (Map)  Onoclea sensibilis                       SENSITIVE FERN
2024 (Map)  Ononis spinosa                           REST HARROW
2025 (Map)  Onopordum acanthium                      Scotch Cottonthistle
2026 (Map)  Onosmodium hispidissimum                 MARBLESEED
2027 (Map)  Onosmodium molle                         MARBLESEED
2028 (Map)  Onosmodium molle occidentale             MARBLESEED
2029 (Map)  Ophioglossum engelmannii                 ADDER'S-TONGUE FERN
2030 (Map)  Ophioglossum vulgatum pseudopodum        ADDER'S-TONGUE FERN
2031 (Map)  Ophioglossum vulgatum pycnostichum       ADDER'S-TONGUE FERN
2032 (Map)  Opuntia fragilis
2033 (Map)  Opuntia humifusa                         PRICKLY-PEAR
2034 (Map)  Opuntia macrorhiza                       BIGROOT PRICKLY-PEAR
2035 (Map)  Ornithogalum nutans                      STAR-OF-BETHLEHEM
2036 (Map)  Ornithogalum umbellatum                  COMMON STAR-OF-BETHLEHEM
2037 (Map)  Orobanche fasciculata                    CLUSTERED BROOMRAPE
2038 (Map)  Orobanche ludoviciana                    BROOMRAPE
2039 (Map)  Orobanche ramosa                         BROOMRAPE
2040 (Map)  Orobanche uniflora                       CANCER-ROOT
2041 (Map)  Orthilia secunda                         ONE-SIDED PYROLA
2042 (Map)  Oryzopsis asperifolia                    MOUNTAIN RICE
2043 (Map)  Oryzopsis pungens                        MOUNTAIN RICE
2044 (Map)  Oryzopsis racemosa                       BLACK-SEEDED RICE GRASS
2045 (Map)  Osmorhiza claytonii                      SWEET CICELY
2046 (Map)  Osmorhiza longistylis                    ANISE-ROOT
2047 (Map)  Osmorhiza longistylis villicaulis        SWEET CICELY
2048 (Map)  Osmunda cinnamomea                       CINNAMON FERN
2049 (Map)  Osmunda claytoniana                      INTERRUPTED FERN
2050 (Map)  Osmunda regalis spectabilis              REGAL FERN
2051 (Map)  Ostrya virginiana                        HOP HORNBEAM
2052 (Map)  Oxalis corniculata                       CREEPING WOOD SORREL
2053 (Map)  Oxalis dillenii                          YELLOW WOOD SORREL
2054 (Map)  Oxalis illinoensis                       ILLINOIS WOOD SORREL
2055 (Map)  Oxalis stricta                           YELLOW WOOD SORREL
2056 (Map)  Oxalis violacea                          PURPLE OXALIS
2057 (Map)  Oxydendrum arboreum                      SOURWOOD
2058 (Map)  Oxypolis rigidior                        COWBANE
2059 (Map)  Oxypolis rigidior ambigua                COWBANE