Grindelia howellii

In Flora of North America, Grindelia howellii Steyermark is recognized at the species level, but with a note that the taxonomic rank should be reconsidered, based on its similarity to plants having been called G. paysonorum H. St. John, or varieties of G. nana Nutt. which were in the Flora of North America treatment considered to be within the wide ranging G. hirsutula (Flora of North America Editorial Committee 2006). Most recently, it has been retained at the species level, but is considered to be a synonym of the elevated Grindelia paysonorum H. St. John, which was known only from Nez Perce County, Idaho, but has a wider range in Idaho and western Montana when it includes Grindelia howellii (Bartoli and Tortosa 2012, Montana Natural Heritage Program 2022).

Grindelia howellii is endemic to western Montana and Idaho, it is known from more than 100 occurrences in Missoula and Powell Counties, Montana, and Benewah County, Idaho. Some occurrences in Montana are on the Blackfoot-Clearwater Wildlife Management Area. It also occurs on the Lolo National Forest in Montana, and from the St. Joe Ranger District of the Idaho Panhandle National Forests. Some occurrences in Montana are on the Blackfoot-Clearwater Wildlife Management Area. It also occurs on the Lolo National Forest in Montana, and from the St. Joe Ranger District of the Idaho Panhandle National Forests. It is threatened by invasive exotic plants, herbicides commonly used for roadside vegetation management, motorized recreation, road construction and widening, and residential development.

Grindelia howellii occurs in the northwestern United States, it is regionally endemic to western Montana and Idaho (Bartoli and Tortosa 2012, Flora of North America Editorial Committee 2006). It is known from Missoula and Powell Counties, Montana, and Benewah County, Idaho (Montana Natural Heritage Program 2022, NatureServe 2022), but it has also been reported from collections in other counties in Idaho (SEINet 2022). The range extent is estimated to be 18,000 but could be 95,000 square kilometers, by including the additional collection records from Idaho (SEINet 2022).

There are estimated to be over 100 occurrences, based on 314 observations, which constitute over 100 mapped occurrences verified since 1990 in Montana and three occurrences in Idaho, plus some additional locations of collections in Idaho (Montana Natural Heritage Program 2022, NatureServe 2022, SEINet 2022).

Howell’s Gumweed is a short-lived perennial which grows in transition areas between grassland and wet meadows and riparian areas, which often coincide with roads, and are areas prone to non-native plant colonization. Weeds or invasive exotic plants species are reported to occur at nearly every population. It can also benefit from some disturbance. Howell's Gumweed is reported to have a strong negative response to chemical herbicide, so the control of exotic plants may further damage populations in the vicinity. Several populations are presumed lost following road maintenance activity and/or herbicide application. Road construction, rerouting or widening are also threats. Other threats include motorized recreation activities, and land-use change for residential development (Montana Natural Heritage Program 2022).