Weeds of Boise: iNaturalist Observations

So far, the lists of weeds at each of the Weeds of Boise sites look pretty similar, with several weed species showing up at nearly every site and other species only occasionally making an appearance. This isn’t a surprise really. The flora of any region typically has several species that are dominant, along with species that occur less frequently. Wild urban flora – or in other words, the naturalized weeds in urban areas – may follow a similar pattern. My unscientific and infrequent surveys, all of which have been pretty close to where I live, aren’t yet representative of the Boise area as a whole. However, something like iNaturalist might help with that. For this reason, I took a look at iNaturalist observations to get a better idea as to which species dominate the wild urban flora of Boise, Idaho.

iNaturalist is a website and app that allows users to identify, map, and share observations of living things with the rest of the world. It has been in use for over a decade and is easily one of the most popular community science, biodiversity mapping, and identification apps around. Even though it is not the primary mission of iNaturalist, the information gathered from user observations is frequently used in scientific research and conservation efforts. With over 80 million observations worldwide, iNaturalist offers a pretty decent picture of the plants, animals, fungi, and other living things found in just about any given location. You don’t even need to a registered user to browse the observations and find out what has been spotted near you or across the globe.

In order to come up with a list of weeds that have been observed in Boise by iNaturalist users, I entered “Boise City Metropolitan Area, ID, USA” into the Location field. It is possible to narrow your search to individual neighborhoods or even broaden your search to include a larger area. Clicking on the map allows you to see the area represented in your search. For my purposes, I figured that the number of observations would change if the area covered was either smaller or larger, but the list of weed species would largely remain the same. After you select your search area, you can filter out the results. Clicking on the plant icon limits the search to plants. At first I selected only introduced plants, but that seemed to eliminate a few of the plants that I would consider weeds, so instead I scanned through the entire list of plants and made a list of each of the weed species and how many times each had been observed.

There are of course limitations to using iNaturalist to create species lists, the main one being that you are relying on decisions made by iNaturalist users when it comes to what gets reported. In my case, in which I’m looking for a list of weed species found in Boise, I know there are plenty of weeds that iNaturalist users either aren’t noticing or aren’t bothering to report. The reported observations are also not likely to match the frequency at which they occur in the environment. Still, it’s interesting to see what gets reported and how often. It’s also interesting to see reports of things that I haven’t seen before. By clicking on individual observations, you can see where those observations were made, which means I know where I can go to find species I haven’t yet encountered.

What follows is a list of the top 25 weeds in the Boise area based on the number of iNaturalist observations, along with photos of some of the most reported weeds. A few of the species on the list, like cornflower, straddle the line between weed and desirable plant. I included them anyway because they are known to be naturalized outside of garden borders, even though some of the reported observations may have been intentionally planted within garden borders.

bittersweet nightshade (Solanum dulcamara)
pink-flowered field bindweed (Convolvulus arvensis)
great mullein (Verbascum thapsus)

Top 25 Weeds in the Boise City Metropolitan Area According to iNaturalist Observations (as of September 21, 2021)

  1. great mullein (Verbascum thapsus) – 110 
  2. common dandelion (Taraxacum officinale) – 98
  3. redstem stork’s-bill (Erodium cicutarium) – 83
  4. chicory (Cichorium intybus) – 62
  5. heart-podded hoary cress (Lepidium draba) – 61
  6. cornflower (Centaurea cyanus) – 58
  7. rush skeletonweed (Chondrilla juncea) – 56
  8. purple loosestrife (Lythrum salicaria) – 49
  9. bittersweet nightshade (Solanum dulcamara) – 47
  10. alfalfa (Medicago sativa) – 46
  11. common soapwort (Saponaria officinalis) – 43
  12. dwarf mallow (Malva neglecta) – 42
  13. donkey tail (Euphorbia myrsinites) – 40 
  14. poison hemlock (Conium maculatum) – 39
  15. field bindweed (Convolvulus arvensis) – 39 
  16. bulbous meadow-grass (Poa bulbosa) – 39
  17. yellow salsify (Tragopogon dubius) – 38
  18. crested wheatgrass (Agropyron cristatum) – 37 
  19. cheatgrass (Bromus tectorum) – 36
  20. moth mullein (Verbascum blattaria) – 36 
  21. hound’s-tongue (Cynoglossum officinale) – 31
  22. Virginia creeper (Parthenocissus quinquefolia) – 30
  23. catnip (Nepeta cataria) – 29
  24. white clover (Trifolium repens) – 29
  25. yellow iris (Iris pseudacorus) – 28
Virginia creeper (Parthenocissus quinquefolia)
catnip (Nepeta cataria)
common soapwort (Saponaria officinalis)

Weeds of Boise: Northwest Corner of Ann Morrison Park

The Boise River, which winds its way through the City of Boise, is flanked by a series of parks known collectively as the Ribbon of Jewels, named in honor of prominent women in the community. Most of these parks are vast expanses of turfgrass scattered with large trees and are meticulously maintained, except near the river where the vegetation is allowed to run a little wild. It is within these narrow strips of land, bordered on one side by the river and the other by regularly mowed turfgrass, that a veritable nature walk can be had right in the heart of the city.

While a few native plant species can be found in these strips, much of the vegetation is introduced. Some of the non-native trees and shrubs may have been intentionally planted, while others came in on their own. Most of the grasses and forbs in the understory are weedy plants commonly seen on all manner of disturbed lands. There are also, of course, a few weeds specific to riparian areas. Due to the wild nature of these strips and the abundance of introduced plants, the river’s edge makes for a great place to become acquainted with our wild urban flora.

Looking at the northwest corner of Ann Morrison Park from the Americana Boulevard Bridge

Because these parks (which include the Boise River Greenbelt) stretch for miles through the city, practically any spot along the way could be a good place to look for weeds. I chose to narrow my search to the northwest corner of Ann Morrison Park. What follows are a few images of some of the plants I found there, along with a list of what I was able to identify during my brief visits this spring. The list will surely grow as I check back from time to time. If you’re interested in learning more about the Boise River and its importance – not just to the humans who call Boise home, but also to myriad other living organisms – check out Boise River Enhancement Network and the work that they are doing to help protect and preserve this invaluable ecosystem.

yellow flag iris (Iris pseudacorus)

Russian olive (Elaeagnus angustifolia)

common mullein (Verbascum thapsus)

climbing nightshade (Solanum dulcamara)

cleavers (Galium aparine)

a strip of cheatgrass (Bromus tectorum)

seed head of dandelion (Taraxacum officinale)

western salsify (Tragopogon dubius)

bull thistle (Cirsium vulgare)

Amur honeysuckle (Lonicera maackii)

creeping buttercup (Ranunculus repens)

Weeds found at the northwest corner of Ann Morrison Park (while several of the trees and shrubs at this location are introduced, I only included those species that are generally considered to be weedy or invasive):

  • Amorpha fruticosa (false indigo bush)
  • Anthriscus caucalis (bur chervil)
  • Arctium minus (common burdock)
  • Bromus tectorum (cheatgrass)
  • Capsella bursa-pastoris (shepherd’s purse)
  • Cerastium vulgatum (mouse-ear chickweed)
  • Cirsium arvense (creeping thistle)
  • Cirsium vulgare (bull thistle)
  • Chondrilla juncea (rush skeletonweed)
  • Convolvulus arvensis (field bindweed)
  • Conyza canadensis (horseweed)
  • Descurainia sophia (flixweed)
  • Elaeagnus angustifolia (Russian olive)
  • Erodium cicutarium (redstem filaree)
  • Euonymus fortunei (winter creeper)
  • Galium aparine (cleavers)
  • Hordeum murinum ssp. glaucum (smooth barley)
  • Iris pseudacorus (yellow flag iris)
  • Lactuca serriola (prickly lettuce)
  • Lamium amplexicaule (henbit)
  • Lonicera maackii (Amur honeysuckle)
  • Malva neglecta (common mallow)
  • Medicago lupulina (black medic)
  • Parthenocissus quinquefolia (Virginia creeper)
  • Plantago sp. (plantain)
  • Poa bulbosa (bulbous bluegrass)
  • Polygonum aviculare (prostrate knotweed)
  • Ranunculus repens (creeping buttercup)
  • Rumex crispus (curly dock)
  • Sisymbrium altissimum (tumble mustard)
  • Solanum dulcamara (climbing nightshade)
  • Sonchus sp. (annual sow thistle)
  • Taraxacum officinale (dandelion)
  • Tragopogon dubius (salsify)
  • Trifolium repens (white clover)
  • Ulmus pumila (Siberian elm)
  • Verbascum thapsus (common mullein)

Like all posts in the Weeds of Boise series, this will be updated as I identify and photograph more of the weeds found in this location.