Montana Field Guide

Spalding's Catchfly is a perennial with a simple or branched rootcrown. There are 4-7 pairs of sessile, broadly lance-shaped leaves that are 6-7 cm long below and gradually reduced in size upward. Herbage is long-hairy and very sticky. There are few to many flowers in a leafy, somewhat open inflorescence. The tubular calyx is ca. 15 mm long, has 10 nerves on its surface, and is very sticky. The corolla has 5 separate, white petals, each composed of a narrow claw that is ca. 15 mm long expanding into a broadened blade above. Only the entire or shallowly-lobed blade with 4 tiny wings at the base protrudes beyond the mouth of the calyx. The fruit is a capsule that is 10-15 mm long and filled with numerous tiny seeds.

Flowering in July and usually continuing through August. Dried flower/fruiting stalks are often visible into the Fall.

This species can be distinguished from other perennial Silene spp. by its very sticky foliage and by its petals that are entire or only shallowly lobed.

Open, mesic grasslands in the valleys and foothills usually with rough fescue, Nelson's needlegrass, Richardson's needlegrass and Idaho fescue. Occasionally with scattered ponderosa pine or broadleaf shrubs. Soils are usually deep and loamy. S. spaldingii typically occurs on northerly aspects and along draws and swales.

1. Reproductive Biology and Phenology: Silene spaldingii is a perennial herb capable of living at least five years (Lesica 1997) and is dependent solely on reproduction from seed. Flowers are perfect and protandrous (anthers mature, dehisce pollen and wither before the styles expand and stigmas become receptive) (Lesica 1993). This reproductive strategy limits, though does not exclude, self-pollination. Seeds apparently germinate in the spring and continue to grow while soil moisture is adequate and temperatures are moderate. Plants have been observed as early as May 22 at Dancing Prairie (Lesica 1997). Aboveground parts of the seedling plants/rosettes dry up and are senescent during the hottest, driest parts of the summer. Plants may then revive with the onset of cool, moist weather in the fall (Lesica 1988). Flowering may take place during or after the second year with flowers developing in July and August. Each open flower persists for two or more days, and several flowers may be in bloom on the same plant allowing for pollination to occur from flowers on the same plant (geitonogamy). Individual plants flower for 2-3 weeks. Fruits of dehiscent capsules contain up to 150 seeds and mature primarily in August (Lesica 1993). Seeds require a short cold treatment for effective germination and may germinate in the fall as well as the spring following as little as four weeks of cold treatment (Lesica 1993, 1999).

The pollination biology of S. spaldingii has been studied by Lesica (1993) and Lesica and Heidel (1996). In Montana, the only pollinators observed visiting S. spaldingii plants were bumblebees (Bombus fervidus). Studies of S. spaldingii pollinators in Montana are limited to the Dancing Prairie population. As noted earlier, self-pollination is possible, though Lesica's study (1993) showed very highly reduced levels of fitness for progeny of close-pollinated flowers (bagged plants) versus open-pollinated flowers.

Potential and Known Pollinators:
The following animal species have been reported as pollinators of this plant species or its genus where their geographic ranges overlap: Bombus vagans, Bombus pensylvanicus, and Bombus impatiens (Colla and Dumesh 2010).

2. Species Ecology: Silene spaldingii occupies mesic sites within Palouse grasslands. Generally, plants are found on northerly aspects, in swales or along small draws where it is presumed more moisture remains available during the hot, dry summer months of July and August. S. spaldingii is atypical in that it flowers in July and August in a habitat when most other species have already completed flowering for the season. One potential advantage of this strategy is that it is not competing for pollinators. However, precipitation is usually scarce during this time period resulting in unfavorable soil moisture conditions for plant growth. Potentially in response to these dry conditions, S. spaldingii plants may remain dormant in some years. It is unclear if this dormancy is a response to the reduced moisture availability in the previous year, dry conditions during part of the current growing season, some combination of these or to some other factor (Lesica 1999, Lesica and Steele 1994). To date, a correlation between precipitation patterns and dormancy has not been made, though plants do apparently show a strong biennial periodicity (Lesica 1997). On-going demographic monitoring conducted by Lesica should help provide answers.

At Dancing Prairie, Lesica (1997) found that an average of 41% of S. spaldingii plants between 1989 and 1994 exhibited annual dormancy and that dormancy rates ranged from 11% in 1989 to 74% in 1994. Dormancy lasted one year in 75% of the observed episodes and no more than two years in 90% of the cases. The study also found that plants spent nearly half their summers in a dormant condition during the six year period. [from Mincemoyer 2005]

STATE THREAT SCORE REASON
Reported threats to Montana's population of Spalding’s Catchfly primarily concern invasive non-native species found at all population locations. Noxious weeds including Sulphur Cinquefoil (Potentilla recta), Spotted Knapweed (Centaurea stoebe), Canada thistle (Cirsium arvense), Common St. John's-wort (Hypericum perforatum), Dalmatian Toadflax (Linaria dalmatica), and Wiregrass (Ventenata dubia) are present and expanding at many Spalding’s Catchfly sites. Co-occurring noxious species are difficult to control and have destructive negative feedback impacts on native populations. Chemical herbicides used to control invasive plant outbreaks directly destroy individuals and expand habitat degradation. At least two populations are extirpated following a severe invasion. Other reported threats include livestock grazing and fire suppression. Ground disturbance from livestock trampling aids the spread of non-natives. Fire suppression is a reported threat known for negative impacts to Spalding’s Catchfly recruitment and survival (MTNHP Threat Assessment 2021).