Diagnostic Characteristics
Cauline leaves 1-3, deeply palmately lobed; flowers regular symmetrical, sepals showy, petaloid; petals very small, 15-20. Pistils forming follicles.
Two subspecies are recognized; T. laxus ssp. albiflorus (Gray) Love, Love and Kapoor has white to cream rather than pale greenish yellow sepals. Gray (1862), Rydberg (1900), and Hitchcock (1964) described T. laxus ssp. albiflorus as having broader sepals as well. However, Doroszewska (1974) in his taxonomic treatment of the genus, found that T. laxus ssp. albiflorus may have both broader and narrower sepals. The latter subspecies is less rare and ranges from British Columbia and Alberta in Canada south in the mountains in Washington, Montana, Wyoming, Colorada and Utah.
Habitat
Trollius laxus grows in wetlands influenced by cold, highly alkaline groundwater seepage. It is found in open fens, along swamp margins, and in partly sunny, wet openings in seepage swamps. In the opinion of Tom Rawinski (pers. comm., s.d.), T. laxus is an obligate calcicole under natural conditions. Swamp populations tend to be rather widely spaced and patchy, but can be large. T. laxus reaches its greatest density in sloping fens. Here, individuals grow either on sedge tussocks somewhat above the saturated soils, or on seepy mineral soil. In seepage swamps, it grows alongside wet depressions or on sedge tussocks. Soils at the Mahoning Co., Ohio population (pH range of 5.9 to 6.7) are not highly organic, and have a high percentage of available carbonates due in part to a limestone formation on surrounding higher ground (Parsons and Yates 1984).
In sloping fens commonly associated species are: Acer rubrum, Aster puniceus, A. umbellatus, Bromus ciliatus, Calamagrostis canadensis, Carex aquatilis, C. flava, C. hystricina, C. interior, C. lacustris, C. leptalea, Chelone glabra, Cicuta maculata, Cirsium muticum, Clematis virginiana, Cornus racemosa, C. stolonifera, Cypripedium reginae, Epilobium leptophyllum, Equisetum arvense, Eriophorum viride-carinatum, Eupatorium maculatum, Fragaria virginiana, Galium sp., Geum rivale, Iris versicolor, Juncus sp., Liparis loeselii, Lycopus sp., Mentha arvensis, Muhlenbergia glomerata, Pinus strobus, Prunella vulgaris, Rhamnus alnifolia, Rubus pubescens, Senecio aureus, Smilacina stellata, Solidago patula, Symplocarpus foetidus, Thalictrum polygamum, (Vaccinium corymbosum and Hamamelis virginiana on acid hummocks), Viburnum cassinoides, V. recognitum, and Zizea aurea. This list was compiled from three sites, two in NY and one in CT.
In seepage swamps commonly associated species are Acer rubrum, Caltha palustris, Carex stricta, Carpinus caroliniana, Galium sp., Geranium maculatum, Geum rivale, Onoclea sensibilis, Osmunda spp., Pinus strobus, Mitella diphylla, Rhamnus alnifolia, Saxifraga pensylvanica, Senecio aureus, Smilacina stellata, Symplocarpus foetidus, Thalictrum polyganum, and Tsuga canadensis. In NY and CT, disjunct populations of northern plants such as Conioselinum chinense, Mitella nuda, and Petasites frigidus sometimes occur in these same wetlands as well as Abies balsamea and Thuja occidentalis (Rawinski personal communication). This list was compiled from six sites; three in Connecticut, one in New York, one in Pennsylvania, and one in Ohio.
Ecology
Trollius laxus flowers from mid-April to mid-May before the canopy trees fully leaf-out. In this regard it behaves like a number of its associated swamp species: Caltha palustris, Cardamine douglasii, Petasites frigidus, Ranunculus septentrionalis, Symplocarpus foetidus, and Viola papilionacea. The seeds which ripen from late May to early July are dispersed passively by gravity with the aid of wind, rain and seasonally high water (Parsons and Yates 1984). Trollius populations increase in size solely by seed (Parsons and Yates 1984), the more vigorous individuals with several flowers producing more seeds. In two independent greenhouse studies, 90% of the seeds collected in the wild germinated when subjected to a 90 day moist, cold period or a moist, cold period coupled with freezing (Parsons and Yates 1984, Brumback 1981). On the other hand, seeds kept in a pit greenhouse without an extended cold period germinated at significantly lower percentages, 8.0% - 2.8% (Parsons and Yates 1984). Seeds are thought to germinate in the wild the following April or May (Parsons and Yates 1984). Under greenhouse conditions, a few seedlings will flower that summer, but the vast majority remain vegetative (Parsons and Yates 1984). In the well maintained population at the Garden in the Woods, some seedlings flower the 2nd year, and most flower the 3rd year (Brumback 1983). No studies have been done on wild populations.
Populations of T. laxus appear to be able to maintain themselves over long periods of time. Field observations throughout its range report that seedlings and mature individuals are present. Furthermore, there are extant populations from which herbarium specimens were collected as early as the 1910s. A number of references in the literature suggest that T. laxus declines as shade increases (Mitchell and Sheviak 1981, Spooner 1981), although these are unsubstantiated reports. Populations of T. laxus growing in open fens tend to have higher densities than populations in seepage swamps, and thus, it is possible that shading decreases population size. However, swamp populations, though scattered, are viable and can be large (Parsons and Yates 1984, Rawinski, pers. comm.). In addition, factors other than shade may contribute to its smaller densities in seepage swamps, e.g., differences in soils, acidity, and moisture availability.