Montana Field Guide

PLANTS: Perennial herbs with basal leaves and an unbranched leafless stem that is 6-13 cm tall. Plants arise from a central rootcrown. Source: Lesica et al. 2012.

LEAVES: The leaves are ascending, all basal and borne on petioles 2-6 cm long. They have linear blades that are 2-5 cm long and 2 mm wide and covered on the upper surfaces with reddish-purple, stalked glands that trap insects. Source: Lesica et al. 2012.

INFLORESCENCE: A 1-sided, nodding, 1 to 4 flowered, raceme-like cyme. Flowers are perfect and have 5 white petals. Source: Lesica et al. 2012.

The specific epithet linearis is a Latin adjective meaning linear. It refers to the linear shape of the leaves. Drosera is derived from the Greek drosos meaning “dewdrops” referring to the dewdrop-like glands on the leaves (Giblin et al. [eds.] 2018).

Flowering late June-August, fruiting in late September.

Montana has 3 Drosera species. All species are insectivorous, perennial herbs that trap prey on their sticky, gland-tipped leaf hairs. The inflorescences of all species are 1-sided, nodding, raceme-like cymes that consist of regular, white flowers. A hand-lens or microscope is required to measure the seeds.

Note that small, young basal rosettes are not particularly reliable or helpful for species identification (Rice 2019).

Slenderleaf Sundew - Drosera linearis, native, SOC
*Size: Mature plants up to 15 cm tall.
*Leaves: Blades are linear, ascending, and 2-5 cm long.
*Capsules: 4-5 mm high.
*Seeds: Round at the tip and less than 1 mm long.
*Flowers: Mature flowers have petals that are 4-8 mm long, a calyx that is 4-5 mm long, and 4 to 5 styles.
*Anthers: Bright orange.

English Sundew - Drosera anglica, native, SOC
*Size: Mature plants are 8-25 cm tall.
*Leaves: Blades are narrowly oblong, ascending, and 10-25 mm long with a 2-6 cm long petiole.
*Capsules: 3-6 mm high.
*Seeds: Pointed at the tip and 1-1.5 mm long.
*Flowers: Mature flowers have petals that are 4-8 mm long, a calyx that is 4-5 mm long, and 4 to 5 styles.
*Anthers: Yellow.

Roundleaf Sundew - Drosera rotundifolia, native, potential SOC
*Size: Mature plants are 3-20 cm tall.
*Leaves: Blades are orbicular, spreading, and 4-12 mm long with a 1-3 cm long petiole.
*Capsules: 3-5 mm high.
*Seeds: Elongate and flat at the tip and about 1.5 mm long.
*Flowers: Mature flowers have petals that are about 6 mm long, a calyx that is just shorter, and usually 3 styles.
*Anthers: White.

Wet, organic soil of nutrient-poor fens in the montane zone. May also occur on lake margins (Rice 2019).

Drosera linearis traps and digests mosquitoes, damsel flies, and other insects (Stromberg-Wilkins 1984).

HYBRIDIZATION
Drosera anglica most likely originated as a hybrid of D. linearis x D. rotundifolia (Wood 1955; Hoyo et al. 2015).

ASSOCIATED SPECIES
Usual associates with Slenderleaf Sundew include Triglochin maritima, Carex chordorrhiza, Carex livida, Lobelia kalmia, and Utricularia minor (Stromberg-Wilkins 1984).

PREY CAPTURE
Prey insects are initially lured to plants by their brilliant red gland stalks (Wolf et al. 2006). This pigmentation may vary due to environmental effects such as sun exposure and inundation (Rice 2019). After landing or climbing onto the leaves, prey get stuck to the longer, trapping glands on the margins of the leaves which hold them in place while the shorter glands secrete digestive enzymes (Lloyd 1942). A bending of the leaf petiole to fold the leaf over itself also assists in keeping prey in place once entrapment has occurred (Darwin 1897).

POPULATION DYNAMICS
Populations of Slenderleaf Sundew examined in Wisconsin have shown a short half-life, rapid turnover of individuals, and unstable growth rates (Stromberg-Wilkins 1984). This suggests that populations are vulnerable to frequent local extinctions. Environmental events that limit seed production such as flooding may threaten population growth. However, it is hypothesized that Slenderleaf Sundew may overcome these incidents by persisting for a season in seed form.

All three Drosera species can reproduce both sexually and vegetatively (Hoyo et al. 2015; Murza et al. 2003). Sexual reproduction is almost exclusively done through self-pollination leading to most offspring being genetically identical to parent plants whether they reproduce sexually or vegetatively (Wolf et al. 2006).

Slenderleaf Sundew reproduces asexually (vegetatively) by producing new raments that sprout from the plants. This occurs when leaf buds separate and form plantlets or when axillary buds form beneath rosettes and then detach when the connecting stem decays (Stromberg-Wilkins 1984).

FRUITS and SEEDS [Lesica et al. 2012; Giblin et al. [eds.] 2018]
Fruits are many-seeded capsules that are 3-5 mm long. Seeds are 0.5-0.8 mm long, rhomboidal, bowl-shaped, and rounded at the tip.

FLOWERS [Lesica et al. 2012; Stromberg-Wilkins 1984]
Each flower has a 5-lobed calyx that is 4-5 mm long and 5 separate, oblong, white petals that are usually about 6 mm long. There are 5 stamens and 4-5 styles, which are divided more than half their length. Slenderleaf Sundew is predominantly self-pollinating. Its flowers only stay open for about 3 hours total before they close and self-fertilize.

LIFE CYCLE [Stromberg-Wilkins 1984]
Expansion of winter buds begin in early spring to form a rosette of up to eight leaves. The plants flower in mid-summer and seeds ripen in approximately one month. Seeds germinate in late summer and throughout the next growing season and may reproduce sexually or asexually when one year old.

Preservation of Slenderleaf Sundew populations requires landscape level efforts to minimize human impacts (Stromberg-Wilkins 1984). It has disappeared from apparently pristine sites due to nearby human disturbance and changing landscape dynamics. Protection of historical sites that have existing seed banks may help re-establishment other populations. However, these sites must be closely monitored for changing water levels due to the particular hydrological conditions in which Slenderleaf Sundew seeds are able to germinate.

Cultivation of Slenderleaf Sundew is very difficult compared to other species in this genus. Introduction, even to suitable habitat, is not a reasonable method for management (Rice 2019).

It is suggested that Slenderleaf Sundew possesses a particularly narrow niche, making it more vulnerable to hydrological impacts and changes in water chemistry than other wetland species existing in the same habitats (Stromberg-Wilkins 1984). It also germinates in a narrower range of water potentials making population sizes very sensitive to flooding events. Alteration of habitat to agricultural uses is also a major threat to populations.

STATE THREAT SCORE REASON
Reported threats to Montana's populations of Slenderleaf Sundew are currently assigned as unknown (MTNHP Threat Assessment 2021). Hiking recreation is indicated to be a potential threat to Slenderleaf Sundew or its habitat. Information about the scope and timing of this threat is needed to assess its relative risk to populations.