Physiognomy and Structure: This swamp forest ranges from coniferous to mixed deciduous-coniferous. The tree canopy may be closed but ranges to partially open with multiple canopy gaps, to very open woodland structure. The shrub and herbaceous layers are usually well-developed, and the bryophyte layer is also well-developed over a hummock-and-hollow microtopography.

Floristics: This alliance encompasses swamp forests dominated by Picea rubens, or codominated by Abies balsamea, Acer rubrum, Betula alleghaniensis, Nyssa sylvatica, or Tsuga canadensis, with a shrub layer characterized by Hypericum densiflorum, Ilex montana, Rhododendron maximum, Sorbus americana, Vaccinium angustifolium, Vaccinium corymbosum, Vaccinium myrtilloides, and Viburnum nudum var. cassinoides. Characteristic herbs include Dryopteris campyloptera, Huperzia lucidula, and Oclemena acuminata (= Aster acuminatus). Other associates may include Caltha palustris, Carex leptalea, Carex trisperma, Chelone glabra, Coptis trifolia, Dalibarda repens, Glyceria melicaria, Glyceria striata, Impatiens capensis, and Osmunda cinnamomea. Well-drained hummocks may support Dryopteris intermedia, Gaultheria hispidula, Maianthemum canadense, Oxalis montana, and Vaccinium oxycoccos. Sphagnum spp. (Sphagnum girgensohnii, Sphagnum fallax, Sphagnum palustre, Sphagnum rubellum) and other mosses are abundant in the mucky hollows and blanket the irregular hummocks between seepage hollows. Other bryophytes include Bazzania trilobata, Polytrichum spp. and Hypnum imponens (Byers et al. 2007).

Dynamics:  These wetlands arose as headwater streams underlain by resistant bedrock and rock outcrops that form natural dams. The saturated hydrology and cold-air drainage from surrounding hills supports a flora more typical of northern regions (Byers et al. 2007).