Rhynchospora mesoatlantica A.Eberly & Naczi, 2023

Treher Eberly, Amanda & Naczi, Robert F. C., 2023, Rhynchospora mesoatlantica (Cyperaceae), an imperiled new species of beaksedge from eastern U. S. A., PhytoKeys 236, pp. 65-81 : 65

Rhynchospora mesoatlantica A.Eberly & Naczi sp. nov.

Figs 2 , 3 , 4

Type.

U.S.A., Delaware: Sussex County, 2 mi E of Bayard, Assawoman Wildlife Area , 29 Sep 2007, A. Treher 84 & R. Naczi (holotype: NY [measured for morphometric analyses]; isotypes: DOV, PH, US).

Diagnosis.

Rhynchospora mesoatlantica is similar to R. filifolia and R. harperi , but R. mesoatlantica differs by its fruit dimensions, scales intermediate in length between R. filifolia and R. harperi , and relatively long fruit stipe. In R. mesoatlantica , scales are 3.0-3.4 mm long, and tubercles are 0.6-0.7 mm long and 26-32% of fruit length, in contrast to R. harperi , which has scales 3.8-5.0 mm long, and tubercles 0.7-1.0 mm long and (30-)33-39(-45)% of fruit length. In R. mesoatlantica , scales are 3.0-3.4 mm long, and fruits are 2.1-2.3 mm long and 0.9 mm wide, in contrast to R. filifolia , which has scales 2.1-3.0 mm long, and fruits 1.5-1.9 mm long and 0.6-0.8 mm wide. Rhynchospora mesoatlantica has fruit stipes 0.29-0.38 mm long, in contrast to R. filifolia (0.16-0.34 mm long) and R. harperi (0.20-0.35 mm long).

Description.

Culm (2-)3-9 dm tall, 0.4-1.2 mm wide at midpoint, erect. Leaves filiform, flexuous; proximal leaf blades 7-25 cm long, 0.2-0.6 times the culm height, 0.5-0.8 mm wide, margins involute; cauline leaf blades 9-21 cm long, 0.5-1.5 mm wide, margins involute. Infructescence composed of 1-3 (-4) compound fascicles per culm. Fascicles hemispheric to occasionally turbinate, 1.0-2.0 cm wide, composed of 5-75 spikelets, branches of subfascicle 0.3-0.9 cm long, 0.2-0.3 mm wide; distalmost fascicle bracts 1-3, 2-13 cm long, 1-1.5 mm wide. Spikelets 3.6-4.7 mm long, proximal scales 1.5-2 mm long, scales from middle of spike 3.0-3.4 mm long, cinnamon brown with darker brown central nerve. Perianth bristles 6, the longest per fruit 2.0-2.4 mm long, 0.8-1.1 times as long as fruit (including tubercle), antrorsely barbellate. Fruit (including the tubercle) 2.1-2.3 mm long, 0.85-0.93 mm wide, bearing persistent perianth bristles; body 1.5-1.7 mm long, obpyriform in outline, surface shiny, smooth, brown or reddish-brown except for whitish and well-demarcated central disk on each face, central disk occupying 0.4-0.8 of fruit width; tubercle with straight or slightly concave margins, 0.56-0.70 mm long, 0.26-0.32 of fruit length, 0.6-0.7 mm wide at base; stipe 0.29-0.38 mm long.

Etymology.

We name Rhynchospora mesoatlantica for the Mid-Atlantic region of the U.S.A., the region in which all known populations occur.

Geographic distribution.

Rhynchospora mesoatlantica is a narrow endemic of a portion of the Mid-Atlantic U.S.A. (Fig. 5 ). It is known only from southern New Jersey, southern Delaware, and southeastern Maryland, where it occurs on the Coastal Plain physiographic province. Specimens document its occurrence from a total of 12 populations, each separated by at least 1 km from other populations. Two of the populations in the vicinity of Ellendale, Delaware [E of Ellendale, Commons s.n. (PH); S of Ellendale, McAvoy 6333 (DOV) and later collections] are sufficiently close (3 km apart) that they map as one population (Fig. 5 ). Other populations are separated by greater distances. The greatest distance separating nearest neighbors among populations (Moyer G0272 in Cape May County, New Jersey, and Commons s.n. in Sussex County, Delaware) is 70 km.

Habitat.

Rhynchospora mesoatlantica grows on the sunny, moist upper portions of natural, shallow, nutrient-poor, seasonal ponds and depressions with gently sloping shorelines and sandy-peaty soils (Fig. 6 ). Surrounding these wetlands are dry-mesic forests or pine plantations. Water levels are typically highest in winter and spring, which is characteristic of Coastal Plain ponds ( Phillips and Shedlock 1993). By the time of fruiting, the ponds are usually devoid of standing water, and the plants grow in soils that are merely moist. At most sites we visited, natural seasonal fluctuations in water levels were disrupted by extensive ditching and draining that apparently lowered the water table. Drier soils throughout the year have provided favorable growing conditions for woody vegetation, which is slowly overgrowing and shading some of the sites. The least disturbed site had few trees and shrubs (Fig. 6 ). In the absence of the natural disturbance of fluctuating water levels, management appears necessary to maintain a sunny environment. Rhynchospora mesoatlantica may persist vegetatively or in the seed bank during periods of unfavorable conditions, but research is needed to understand its persistence and dormancy.

Close plant associates (those growing within 10 m) of Rhynchospora mesoatlantica are Acer rubrum L., Boltonia asteroides (L.) L’Hér. (Treher 75 & Naczi, DOV), Cladium mariscoides (Muhl.) Torr. (Treher 74 & Naczi, DOV), Coelorachis rugosa (Nutt.) Nash (Naczi 12056 & Treher, DOV, PH; Treher 72 & Naczi, DOV), Coleataenia longifolia (Torrey) Soreng ssp. longifolia , Dichanthelium spretum (Schult.) Freckmann (Naczi 12057 & Treher, NY, PH), Eleocharis tenuis Schult., Hypericum denticulatum Walter (Naczi 12058 & Treher, DOV), Juncus canadensis J.Gay in Laharpe (Naczi 12064 & Treher, NY; Treher 82 & Naczi, DOV), Juncus repens Michx. (Naczi 12062 & Treher, NY; Treher 78 & Naczi, DOV), Kellochloa verrucosa (Muhl.) Lizarazu, Nicola, & Scataglini (Treher 116 & Naczi, DOV), Proserpinaca pectinata Lam. (Treher 79 & Naczi, DOV), Rhexia aristosa Britton (Naczi 12065 & Treher, DOV), Rhexia virginica L. (Treher 118 & Naczi, DOV), Rhynchospora chalarocephala Fernald & Gale (Naczi 12086 & Treher, NY; Treher 112 & Naczi, DOV), Rhynchospora filifolia (Naczi 12060A & Treher, NY; Treher 84a & Naczi, DOV), Rhynchospora gracilenta A.Gray (Treher 113 & Naczi, DOV), Rhynchospora inundata (Oakes) Fernald (Naczi 12061 & Treher, DOV), Saccharum giganteum (Walter), Scleria reticularis Michx. (Naczi 12063 & Treher, NY; Treher 77 & Naczi, DOV), Sclerolepis uniflora (Walter) Britton, Sterns, & Poggenb. (Naczi 12059 & Treher, DOV; Treher 73 & Naczi, DOV), and Sphagnum macrophyllum Bernh. ex Brid. Pers.

Preliminary conservation assessment.

Rhynchospora mesoatlantica is at a high risk of extinction due to a restricted geographic range, small number of occurrences, small population sizes, and historic and ongoing declines due to numerous threats. All historic and current populations total 12. Six of the populations have not been seen for over 20 years, despite repeated, more recent surveys at most of the sites. Three of these populations had been documented in the 1990s, yet we could not relocate them. Thus, declines are apparent in number of populations and number of plants. We are sufficiently familiar with some of these sites to identify likely causes for extirpations: habitat destruction for some and, for others, habitat degradation, including changes to hydrology.

Only six populations are known to be extant. Populations are typically small, ranging from 25 to a maximum of 200-300 plants at the population northwest of Belleplain (R. Moyer, pers. comm.). Only three populations contain more than 100 plants. Our estimate of the total number of mature plants present in extant populations is 700.

Five of the six populations known to be extant are in protected areas. Most of these protected areas are state forests that allow resource extraction and consequent habitat alteration.

Most extant and historic occurrences are/were in Coastal Plain ponds in Delaware and Maryland, one of the most threatened habitats on the Delmarva Peninsula and host to many rare species ( McAvoy and Bowman 2002). Most of these ponds and surrounding forests are highly degraded due to direct and indirect anthropogenic impacts. Land-use changes resulting in habitat fragmentation, conversion of forest to pine plantations, destructive forestry practices like clear-cutting, and hydrologic alterations due to extensive ditching and draining are among the threats contributing to past and ongoing declines ( McAvoy and Bowman 2002). Quantifying declines in Rhynchospora mesoatlantica is challenging; the historic record is sparse, with only four populations documented prior to 1990. Landscape changes are evident throughout the Delmarva Peninsula, including the extent of ditching and draining. In Delaware alone, there are over 2,000 miles of ditches intended to redirect normal water flows across the land and sustain productive agricultural lands (DE DNREC 2023). Unfortunately, these ditches negatively impact natural plant communities hosting R. mesoatlantica by interrupting seasonal water-level fluctuations that suppress woody vegetation. Habitat restoration with ongoing maintenance, especially for natural hydrologic cycles, appears to be warranted at most sites, including those on public lands.

Also noteworthy is the fact that R. mesoatlantica plants usually occupy only a portion, and often a small portion, of the Coastal Plain ponds that host this species. For example, the area of one pond is 0.008 km2 (8,000 m2), yet plants of R. mesoatlantica occupy only 0.004 km2 (4,000 m2) of the pond. Our estimate of the area occupied by all known R. mesoatlantica populations, historic and extant, is 0.031 km2 (31,000 m2). For R. mesoatlantica populations known to be extant, our estimate of area occupied is 0.017 km2 (17,000 m2).

Due to decades-long recognition of Coastal Plain ponds as centers of rare plant diversity (e.g., Hirst 1983; Boone et al. 1984; McAvoy and Bowman 2002) and our own extensive field efforts to rediscover formerly documented populations of Rhynchospora mesoatlantica and discover new ones, we regard the likelihood of discovery of new populations as low. Simply, most Coastal Plain ponds within the geographic range of R. mesoatlantica have been botanically explored, many very extensively during multiple years and multiple seasons.

We recommend a NatureServe Global Rank of Critically Imperiled (G1, Faber-Langendoen et al. 2012) for Rhynchospora mesoatlantica , based on considerations of rarity, threats, and trends ( Master et al. 2012). There are 12 known occurrences (6 historic and 6 extant), a Range Extent (Extent of Occurrence, EOO) of 4,495 km2, and an Area of Occupancy (AOO) of 44 km2. Threat impact is estimated at very high, and short-term trends and long-term trends are estimated to be at least 10% and 40%, respectively, based on declines in AOO, population size, and number of occurrences.

As a preliminary assessment, we consider the IUCN category Endangered ( IUCN Standards and Petitions Committee 2022) to apply to Rhynchospora mesoatlantica for the following reasons: EOO of 4,495 km2 is <the 5,000 km2 threshold (B1); AOO of 44 km2 is <the 500 km2 threshold (B2); and we have observed continuing decline in AOO, habitat quality, and number of populations (Bb). Tentatively, we assess the metapopulation as severely fragmented since at least 50% of the populations are isolated and small (<50 plants) and occurring in a very rare and localized habitat surrounded by unsuitable habitats and with limited capacity for dispersal between distant extant populations 11-70 km apart (Ba).

Due to the severity of conservation threats, few known extant populations, small population sizes, and apparent necessity of human-mediated intervention to maintain habitats, we recommend Rhynchospora mesoatlantica for protection under the U.S.A. Endangered Species Act.

Additional specimens examined.

(* = specimen measured for morphometric analyses)- U.S.A. Delaware: Sussex Co., Population 1: E of Bayard, 26 Sep 1986, Hirst 459 (DOV); Assawoman Wildlife Area , 8 Sep 1991, McAvoy s.n. ( US); E of Bayard , Assawoman Wildlife Area , 31 Nov 1991, Hirst 449 (DOV); Assawoman Wildlife Area , 22 Nov 1992, McAvoy 243 (DOV); Assawoman Wildlife Area , 1.7 mi E of Bayard, 11 Nov 1993, Hirst 309 (DOV); Assawoman Wildlife Area , 16 Aug 1995, McAvoy 1234 (DOV); 2 mi E of Bayard, Assawoman Wildlife Area , 29 Sep 2007, Naczi 12060 & Treher (MO, NY, PH). Population 2: E of Ellendale, 17 Aug 1899, Commons s.n. ( PH *). Population 3: S of Ellendale , Redden State Forest tract, N side of Saw Mill Road, E of Spicer Road, 29 Oct 2007, 6333 McAvoy (DOV); Redden State Forest , N side of Saw Mill Road, E of Spicer Road, SE of Ellendale, 5 Aug 2008, McAvoy 6417 (DOV); 4.5 mi W of Milton, 25 Sep 2008, Treher 373 & McAvoy (DOV*); S of Ellendale, N side of Saw Mill Road, 21 Aug 2013, McAvoy 7220 (NY). Population 4: 1.8 mi NNE of Whitesville, 12 Sep 1992, Hirst 415 & Wilson (DOV); 1.8 mi NNE of Whitesville, 12 Sep 1992, Hirst 416 & Wilson (DOV); 1.5 mi N of Whitesville, 27 Jul 1993, Hirst 409 & Wilson (DOV*); SE of Pepperbox, 30 Jul 1997, McAvoy 2765 (DOV). Population 5: 1.8 mi SW of Woodland, 28 Aug 1993, Hirst 410 & Wilson (DOV*) . Maryland: Dorchester Co., Population 6: 1.7 mi NW of Reids Grove, 21 Aug 1998, Hirst 1198 & Wilson (DOV); 0.2 mi SE of junction of Centennial and Kraft Roads, 21 Aug 1998, Hirst 1200 & Wilson (DOV); NW of Reids Grove, 28 Aug 1998, McAvoy 3994 (DOV); 3.4 mi SW of Brookview, 1.8 mi NW of Reids Grove, 29 Aug 1998, Hirst 1208 & Wilson (DOV); 1.8 mi NW of Reids Grove, 3.4 mi SW of Brookview, 29 Aug 1998, Hirst 1209 & Wilson (DOV); 3.3 mi SW of Brookview, 1 Oct 2008, Treher 377 & Knapp (DOV*). Population 7: 1.5 mi SW of Brookview, 20 Sep 1997, Hirst 1189 & Wilson (DOV); W of Brookview, 4 Oct 1997, McAvoy 3160 (DOV*); S of Brookview, 28 Aug 1998, McAvoy 4002 (DOV); 1.4 mi SSW of Brookview, 2.0 mi NNE of Reids Grove, 29 Aug 1998, Hirst 1207 et al. (DOV). Wicomico Co. , Population 8: NE of Mardela Springs, 17 Sep 2000, Hirst 1234 & Wilson (DOV*). Population 9: 1.5 mi W of Wango, 2 Oct 2007, Treher 110 & Naczi (DOV), 1.5 mi W of Wango, SW of junction of Twilleys Bridge Road and Fooks Road, 2 Oct 2007, Naczi 12087 & Treher (NY); S of Twilley’s Bridge Road, W of Powellville, 30 Sep 2014, McAvoy 7465 (DOV*). Worcester Co. , Population 10: 5 mi N of Pocomoke, Pocomoke State Forest , 6 Oct 1984, Hirst 418 (DOV*); N of Pocomoke , Pocomoke State Forest , 22 Aug 1986, Hirst 439 (DOV) . New Jersey: Cape May Co., Population 11: Woodbine , 30 Aug 1900, S. Brown 4289 (NY, PH *); Between Belleplain and Woodbine, 4 Sep 1960, B. Hirst s.n. ( PH). Population 12: NW Belleplain, 24 August 2015, R. Moyer G0272 (NY*) .

Figures

Figure 2. Representative mature fruits of Rhynchospora species. Left to right: Rhynchospora filifolia [Naczi 12060 A & Treher (NY)], R. harperi [Naczi 16347 (NY)], and R. mesoatlantica [Naczi 12060 & Treher (NY)]. Scale bar: 1.0 mm.

Figure 3. Rhynchospora mesoatlantica A habit B distal portion of infructescence C spikelet D distal scale E immature fruit F mature fruit, lateral view, with detail of perianth bristle (left) and top view (below). From Treher 84 & Naczi (Holotype, NY). Scale bars: 2 cm (A); 1 cm (B); 1 mm (C, D, E); 0.5 mm (F).

Figure 4. Habit of Rhynchospora mesoatlantica. Amanda T. Eberly with R. mesoatlantica rooted in habitat at type locality (Treher 84 & Naczi).

Figure 5. Known geographic distribution of Rhynchospora mesoatlantica. Based on all known collections.

Figure 6. Representative habitat of Rhynchospora mesoatlantica. At type locality (Treher 84 & Naczi).