Agoseris tomentosa Howell accepted as Agoseris parviflora (Nutt.) D.Dietr. (original description)
Arnica cernua Howell (original description)
Aster burkei (A.Gray) Howell accepted as Symphyotrichum foliaceum (Lindl. ex DC.) G.L.Nesom (original description)
Aster eatonii (A.Gray) Howell accepted as Symphyotrichum eatonii (A.Gray) G.L.Nesom (original description)
Aster geyeri (A.Gray) Howell accepted as Symphyotrichum laeve (L.) Á.Löve & D.Löve (original description)
Baeria aristosa (A.Gray) Howell accepted as Lasthenia coronaria (Nutt.) Ornduff (original description)
Boltonia occidentalis (A.Gray) Howell accepted as Boltonia asteroides var. recognita (Fernald & Griscom) Cronquist (original description)
Chrysothamnus nanus Howell accepted as Ericameria nana Nutt. (original description)
Chrysothamnus resinosus (Nutt.) Howell accepted as Ericameria resinosa Nutt. (original description)
Erigeron aliceae Howell (original description)
Erigeron aliciae Howell (original description)
Erigeron amplifolius Howell accepted as Erigeron eliceae (original description)
Erigeron pacificus Howell accepted as Erigeron eatonii var. lavandulus Strother & Ferlatte (original description)
Erigeron spathulifolius Howell accepted as Erigeron cascadensis A.Heller (original description)
Eriophyllum lanceolatum Howell accepted as Eriophyllum lanatum var. lanceolatum (Howell) Jeps. (original description)
Eriophyllum leucophyllum Howell (original description)
Helenium autumnale var. grandiflorum Howell (original description)
Hieracium cinereum Howell (original description)
Hieracium longiberbe Howell (original description)
Machaeranthera attenuata Howell accepted as Corethrogyne filaginifolia (Hook. & Arn.) Nutt. (original description)
Machaeranthera eradiata (A.Gray) Howell accepted as Dieteria canescens var. shastensis (A.Gray) D.R.Morgan & R.L.Hartm. (original description)
Pyrrocoma hallii (A.Gray) Howell accepted as Columbiadoria hallii (A.Gray) G.L.Nesom (original description)
Pyrrocoma lanceolata Howell (original description)
Pyrrocoma tenuicaulis Howell (original description)
Senecio adamsii Howell accepted as Packera streptanthifolia (Greene) W.A.Weber & Á.Löve (original description)
Senecio foetidus Howell accepted as Senecio hydrophiloides Rydb. (original description)
Senecio oreganus Howell accepted as Senecio hydrophiloides Rydb. (original description)
Solidago hesperia Howell accepted as Solidago simplex var. nana (A.Gray) G.S.Ringius (original description)
Solidago hesperius Howell (original description)
Stenotus brandegeei (A.Gray) Howell accepted as Erigeron aureus Greene (original description)
Stenotus lyallii (A.Gray) Howell accepted as Tonestus lyallii (A.Gray) A.Nelson (original description)
Wyethia lanceolata Howell accepted as Wyethia amplexicaulis (Nutt.) Nutt. (original description)