Van brunt’s jacob’s-ladder (Polemonium vanbruntiae) COSEWIC assessment and status report: chapter 6

Biology

General

The two most important factors relating to the conservation status of this species are reproductive characteristics and climate conditions. Apparently, Van Brunt’s Jacob’s-ladder seeds can only germinate after a period of cold, dry conditions. However, the plant can also reproduce vegetatively.

Reproduction

Polemonium vanbruntiae can reproduce vegetatively or sexually. Asexual or vegetative reproduction takes place through the branched rhizomes of this perennial plant. In Vermont, E. Thompson (1991) observed that occasionally hundreds of stems can connect in the ground to form a clone covering tens of square feet. This would tend to reduce the number of genetically distinct plants in Quebec populations, where clones also seem to occur.

Sexual reproduction takes place by way of cross-pollination and mainly with the help of insects. Wherry (1935) and Thompson (1991) report that pollination is carried out by honey bees (Apis mellifera) and bumblebees (Bombus sp.). Our observations in 1991 and 1992 (Sabourin and Paquette, 1992, 1994) indicate that several other insects, such as butterflies, and even a bird, the ruby-throated hummingbird (Archilochus colubris) visit the flowers of Polemonium vanbruntiae. This suggests that the species can produce a large quantity of nectar. According to NatureServe (2001), the species is self-sterile.

A very important factor that must be considered is seed germination. In the course of various experiments, Brumback (1989) found that the seeds could not germinate under cold, wet conditions, but would readily germinate after being kept under cold, dry conditions (between September 1986 and April 1987). However, this author does not provide details on how long the seeds were kept before germination and under which temperature, humidity and light conditions they were maintained. Also, the experiences with this species at the Montréal Botanical garden demonstrated a low germination rate of 0 to 15% (A. Meilleur, pers. comm. 2002).

Survival

Little information is available on this subject. The field observations suggest some predation by white-tailed deer (Odocoilus virginianus), which may occasionally browse a few stems, but this does not appear to be an important factor in the plant’s Canadian distribution.

Physiology

Polemonium vanbruntiaereaches its northern limit in Quebec, at about 46° latitude north, at Saints-Martyrs-Canadiens. As the elevation of this site is also the highest in Quebec for the species, almost 65 metres higher than the second highest site, it is possible that the species occurs even further north.

The species seems to have a good ability to adapt to changes in its environment, since it has been found in logging road ditches and agricultural old fields. However, there must be sufficient moisture throughout the growing season, without prolonged flooding or drought. Interestingly, in alder thickets, the species is often found on the mounds forming at the base of alders. According to NatureServe (2001), the plant seems to have a rather wide ecological tolerance, but it has a rather narrow pH range, and open areas with circumneutral springs would represent its ideal habitat. According to Wherry (1935), the pH ranges from circumneutral to slightly acidic.

Van Brunt’s Jacob’s-ladder is a perennial plant that prefers deep rich soils. In Quebec, it flowers for about 5 weeks, approximately from June 20 to July 25, with some year to year variation. The first fruit ripen around mid-August at the latest.

Movements/dispersal

Seed dispersal occurs most readily in winter, when the stems extend above the snow cover, and the seeds can be carried by the wind over the icy crust or the snowy surface; occasionally, the stems can break and roll away with the wind. The distance covered in this fashion may reach several hundred metres.

Nutrition and interspecific interactions

Polemonium vanbruntiaedoes not live as a symbiont or parasite with other species. However, companion plants provide, as they decompose, the organic matter needed to form the rich and deep soils preferred by Van Brunt’s Jacob’s-ladder. Of course, material deposited by rivers and streams or through seepage and run-off is also important in this respect.

Apart from the white-tailed deer, the plant may also be eaten by insects, but this type of negative interaction does not appear to be significant.

Behaviour/adaptability

Van Brunt’s Jacob’s-ladder can tolerate a certain level of habitat modification, but it does not tolerate major changes, such as permanent flooding or soil drying-up. For instance, the population at Saint-Adrien almost disappeared (1 plant observed in 2001) after a nearby road was widened, as this altered the drainage and resulted in prolonged flooding.

At Stoke River, one of the two sites (the one to the north) was mowed and partly ploughed during the late 1990s, and several Jacob’s-ladder plants disappeared. A similar change happened at Saints-Martyrs, because of logging and drainage work.

Transplantation has already been carried out successfully. There are at least 18 living specimens at the Montreal Botanical Garden. At the Garden, a team recently undertook cultivation and germination work on plants having a vulnerable or endangered status in Quebec, and Polemonium vanbruntiae is at the top of their list (A. Meilleur, pers. comm. 2002).

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