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.

Dispersal by Bulbils – A Bulbous Bluegrass Story

The main way that a plant gets from place to place is in the form of a seed. As seeds, plants have the ability to travel miles from home, especially with the assistance of outside forces like wind, water, and animals. They could also simply drop to the ground at the base of their parent plant and stay there. The possibilities are endless, really.

But what about plants that don’t even bother making seeds? How do they get around? In the case of bulbous bluegrass, miniature bulbs produced in place of flowers function exactly like seeds. They are formed in the same location as seeds, reach maturity and drop from the plant just like seed-bearing fruits, and are then dispersed in the same ways that seeds are. They even experience a period of dormancy similar to seeds, in that they lie in wait for months or years until the right environmental conditions “tell” them to sprout. And so, bulbils are basically seeds, but different.

bulbous bluegrass (Poa bulbosa)

Bulbous bluegrass (Poa bulbosa) is a Eurasian native but is widely distributed outside of its native range having been repeatedly spread around by humans both intentionally and accidentally. It’s a short-lived, perennial grass that can reach up to 2 feet tall but is often considerably shorter. Its leaves are similar to other bluegrasses – narrow, flat or slightly rolled, with boat-shaped tips and membranous ligules – yet the plants are easy to distinguish thanks to their bulbous bases and the bulbils that form in their flower heads. Their bulbous bases are actually true bulbs, and bulbous bluegrass is said to be the only grass species that has this trait. Just like other bulb-producing plants, the production of these basal bulbs is one way that bulbous bluegrass propagates itself.

basal bulbs of bulbous bluegrass

Bulbous bluegrass is also propagated by seeds and bulbils. Seeds form, like any other plant species, in the ovary of a pollinated flower. But sometimes bulbous bluegrass doesn’t make flowers, and instead modifies its flower parts to form bulbils in their place. Bulbils are essentially tiny, immature plants that, once separated from their parent plant, can form roots and grow into a full size plant. The drawback is that, unlike with most seeds, no sexual recombination has occurred, and so bulbils are essentially clones of a single parent.

The bulbils of bulbous bluegrass sit atop the glumes (bracts) of a spikelet, which would otherwise consist of multiple florets. They have dark purple bases and long, slender, grass-like tips. Bulbils are a type of pseudovivipary, in that they are little plantlets attached to a parent plant. True vivipary occurs when a seed germinates inside of a fruit while still attached to its parent.

Like seeds, bulbils are small packets of starch and fat, and so they are sought ought by small mammals and birds as a source of food. Ants and small rodents are said to collect and cache the bulbils, which is one way they get dispersed. Otherwise, the bulbils rely mostly on wind to get around. They then lie dormant for as long as 2 or 3 years, awaiting the ideal time to take root.

bulbils of bulbous bluegrass

Bulbous bluegrass was accidentally brought to North America as a contaminant in alfalfa and clover seed. It was also intentionally planted as early as 1907 and has been evaluated repeatedly by the USDA and other organizations for use as a forage crop or turfgrass. It has been used in restoration to stabilize soils and reduce erosion. Despite numerous trials, it has consistently underperformed mainly due to its short growth cycle and long dormancy period. It is one of the first grasses to green up in the spring, but by the start of summer it has often gone completely dormant, limiting its value as forage and making for a pretty pathetic turfgrass. Otherwise, it’s pretty good at propagating itself and persisting in locations where it hasn’t been invited and is now mostly considered a weed – a noxious one at that according to some states. Due to its preference for dry climates, it is found most commonly in western North America.

In its native range, bulbous bluegrass frequently reproduces sexually. In North America, however, sexual reproduction is rare, and bulbils are the most common method of reproduction. Prolific asexual reproduction suggests that bulbous bluegress populations in North America should have low genetic diversity. Researchers set out to examine this by comparing populations found in Washington, Oregon, and Idaho. Their results, published in Northwest Science (1997), showed a surprising amount of genetic variation within and among populations. They concluded that multiple introductions, some sexual reproduction, and the autopolyploidy nature of the species help explain this high level of diversity.

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Interested in learning more about how plants get around? Check out the first issue of our new zine Dispersal Stories.