Introduction

Cape Horn is a crescent shaped hill in Northumberland, Coos County, New Hampshire. Its origin is a ring dike, a geologic phenomenon for which New Hampshire is especially known (Eusden et al., 2013), and the best topographically expressed ring dike in North America (Chapman, 1948). Its composition is hornblende syenite, an uncommon igneous rock that is known for supporting calcium-enriched plant habitats of high diversity and rare species in New Hampshire (Bailey, 2013). Given its location between the upper Connecticut River and the White Mountains, Cape Horn has been ranked as a critical site for biodiversity connectivity. 

A preliminary flora of the Cape Horn State Forest, a 2,221 acre property consisting largely of the southern portion of Cape Horn and adjacent wetlands associated with Dean Brook, was completed by Bowman & Bailey (2007). Since then, additional conservation purchases have protected most of the northern portion of Cape Horn, including a 168 acre expansion of the state forest and the 289 acre Heon Tract by The Nature Conservancy. The present project seeks to provide a complete vouchered vascular flora of all conservation properties at Cape Horn. 

History of botanical work

Botanical collections at Cape Horn began with Arthur Stanley Pease, who collected in Coos County from 1895-1962, culminating in the publication of his seminal vascular flora of the county (Pease, 1964). Over four days between 1917 and 1953, he documented a total of six taxa at the site. On August 12, 1959, he led A. R. Hodgdon, F. L. Steele, and A. Lincoln on a collecting trip where they documented an additional twenty taxa, primarily common, widely distributed species. Most of his collections from Northumberland are labelled as from along the Connecticut River or adjacent railroad grade. Given the small number of specimens labelled Cape Horn, it seems that forays there were limited and not a focus of this work. 

Unusual diversity at Cape Horn, including several state rare and endangered species, was first reported in a survey of Diamond International lands conducted by J. Korpi and N. Conrad in 1968. This led to initial purchase and establishment of Cape Horn State Forest. Detailed inventory and monitoring of rare plants began with a Plant Conservation Volunteer (a program of the New England Wildflower Society) field trip in 1999, with continued surveys through the 2000's by S. Bailey, T. and D. Tellman, I. Baird, J. Hoy, B. Engstrom, and others. 

More targeted research projects began when Sperduto and Bailey (2003) set up several monitoring plots on cliffs at Cape Horn as part of a study of circumneutral cliffs across the White Mountain region. Several vascular and bryophyte vouchers were collected during this study. Bowman and Bailey (2007) conducted an ecological inventory of Cape Horn State Forest which included a preliminary, partially vouchered, vascular flora. Populations of Dryopteris fragrans and Hedyotis longifolia at Cape Horn were included in geographic studies of plant genetic diversity and speciation mechanisms (Bouchard et al., 2017; Glennon & Church, 2015).

The current project seeks to provide a vouchered vascular plant flora for the entire 2,678 acres of conservation land on and surrounding Cape Horn. Field work was conducted on ten dates between June 12 and October 10, 2023, for a total of 20 person days in the field. The rate of new taxa observations did not decline during this period, suggesting that additional taxa remain to be discovered on the site. A companion checklist of nonvascular flora for the site has also been developed, but is quite incomplete at this time (Peters 2024).

In the following list, abundance codes are abbreviated as: C= Common, F= Frequent, O= Occasional, R= Rare, H= Historical (no reports in past 30 years (i.e., since 1991). These represent a loosely exponential series of gradations that are intended to convey the frequency of encountering a species, thus they integrate the known or apparent population size and extent and, for restricted species, the number of discrete patches. In some cases a question mark follows the abundance code indicating an assumed abundance that was less supported by actual observations. A brief description of occupied habitats and distribution follows the abundance code. The checklist is arranged alphabetically by family name.

Of the 522 taxa reported here, 4xx taxa have been vouchered, as of April 1, 2024. Older specimens are cited by collector and herbarium, and are all cataloged in the Consortium of Northeastern Herbaria (CNH) portal. Specimens cited as "Consortium of Northeastern Herbaria" are currently observations in the CNH portal and are expected to be transferred to the Hodgdon Herbarium (NHA) in the near future. Specimen numbers for Bailey and Peters begin with a 2 digit prefix indicating the collection year (ie., 23 = 2023), Engstrom’s numbers begin with a full 8-digit date prefix.

References Cited

Bailey, S. W. (2013). Two fern species new to New Hampshire, with comments on the generation of calcareous-like habitat by base-poor rocks. Rhodora, 115, 286-289.

Bouchard, J. R., Fernando, D. D., Bailey, S. W., Weber-Townsend, J., & Leopold, D. J. (2017). Contrasting patterns of genetic variation in central and peripheral populations of Dryopteris fragrans (Fragrant Wood Fern) and implications for colonization dynamics and conservation. International Journal of Plant Sciences, 178 (8), 607-617.

Bowman, P. J., & Bailey, S. W. (2007). Ecological Inventory of Cape Horn State Forest. New Hampshire Natural Heritage Bureau, Concord, NH.

Chapman, R. W. (1948). Petrology and structure of the Percy Quadrangle, New Hampshire. Geological Society of America Bulletin, 59, 1059-1100.

Eusden, J. D., Thompson, W. B., Fowler, B. K., Davis, P. T., Bothner, W. A., Boisvert, R. A., & Creasy, J. W. (2013). The Geology of New Hampshire's White Mountains. Durand Press, Lyme, N H.

Glennon, K. L., & Church, S. A. (2105). Gene flow contributes to genetic diversity of tetraploid populations of the North America plant genus Houstonia (Rubiaceae). Rhodora, 117, 41-66.

Pease, A. S. (1964). A Flora of Northern New Hampshire. New England Botanical Club, Inc., Cambridge, MA.

Peters, Matthew J. 2024. A Very Preliminary Bryophyte Checklist for Cape Horn, Northumberland, New Hampshire.

Sperduto, D. D., & Bailey, S. W. (2003). Geology and Ecology of Cliffs in the White Mountains of New Hampshire. New Hampshire Natural Heritage Program and USDA Forest Service, Concord, NH.