Exploration of meaningful subspecies definitions of the carnivorous Northern Pitcher Plant (Sarracenia purpurea), throughout its geographic distribution

Abstract

The carnivorous wetland plant, Sarracenia purpurea (the northern pitcher plant) is native to eastern and Midwestern North America. This species is abundant within its habitat but suitable habitat is increasingly scarce, raising interest in S. purpurea restoration and conservation. Complicating conservation planning, two controversial subspecies of S. purpurea are historically defined primarily on morphologic traits: S. purpurea subsp. purpurea distributed north of Maryland and S. purpurea subsp. venosa distributed south of Maryland. S. purpurea is also found in three distinct habitat types defined by substrate: acidic Sphagnum peatlands, acidic sandy savannahs, and alkaline marl wetlands. In species level studies, S. purpurea leaves have exhibited morphological plasticity in response to environmental variability, bringing into question the validity of subspecies definitions based on morphology alone. This study examined morphologic and genetic variation throughout S. purpurea’s natural distribution, encompassing both the traditional subspecies and three unique habitat types testing the validity of traditional subspecies definitions. Genetic analysis indicated possible ecological significance of considering a new grouping of S. purpurea populations into Midwest, N. East Coast and S. East Coast populations (AMOVA % variation = 13.34, P = 0.0078) based on genetic differentiation. Morphological variation in leaf shape measurements supported this division as well as indicating plasticity associated with environmental variables. This study conservatively suggests that new, geographical area conservation units may be a more important conservation unit for preserving S. purpurea genetic variation and morphological plasticity than traditional subspecies definitions.