rough m. _occidentale_ Mackenz. western m. _Oonopsis engelmannii_ (see _Haplapappus_) _Opuntia_ Mill. pricklypear; cholla _arborescens_ Engelm. [_O. imbricata_ (Haw.) DC.] walkingstick c. _fragilis_ (Nutt.) Haw. brittle p. _humifusa_ Raf. common p. _macrorhiza_ Engelm. bigroot p. _polyacantha_ Haw. plains p. _tortispina_ Engelm. twistspine p. _Oreocarya_ (see _Cryptantha_) _Orobanche_ L. broomrape _ludoviciana_ Nutt. Louisiana b. _uniflora_ L. ghostpipe _Osmorhiza longistylis_ (Torr.) DC. longstyle sweetroot _Othake_ (see _Palafoxia_) _Oxalis_ L. oxalis _europaea_ Jord. European yellow o. _stricta_ L. common yellow o. _violacea_ L. violet woodsorrel o. _Oxybaphus_ (included in _Mirabilis_) _Palafoxia spacelata_ (Nutt.) Cory [_Othake s._ (Nutt.) Rydb.] othake _Parietaria pensylvanica_ Muhl. pellitory _Paronychia_ Mill. nailwort _canadensis_ (L.) Wood [_Anychia c._ (L.) BSP.] Canada n. _fastigiata_ (Raf.) Fern. (_Anychia polygonoides_ Raf.) forked n. _jamesii_ T. & G. james n. _Parthenium integrifolium_ L. parthenium _Pastinaca sativa_ L. parsnip _Pectis angustifolia_ Torr. pectis _Pedicularis canadensis_ L. pedicularis _Penstemon_ Mitchell penstemon _albidus_ Nutt. white p. _ambiguus_ Torr. gilia p. _angustifolius_ Nutt. ex Pursh, subsp. _caudatus_ (Heller) Keck narrowleaf p. _buckleyi_ Pennell buckley p. _cobaea_ Nutt. cobaea p. _digitalis_ Nutt. smooth p. _grandiflorus_ Nutt. shell-leaf p. _pallidus_ Small pale p. _tubaeflorus_ Nutt. tube p. _Penthorum sedoides_ L. penthorum _Perideridia americana_ (Nutt.) Reichenb. (_Eulophus a._ Nutt.) eulophus _Perilla frutescens_ (L.) Britt. common perilla _Phacelia_ Juss. phacelia _gilioides_ A. Brand (_P. hirsuta_ of many SW botanists, not Nutt.) hairy p. _integrifolia_ Torr. gyp p. _Phellopterus_ (see _Cymopterus_) _Phlox_ L. phlox