Abstract

A key and checklist are presented for 44 species and 4 varieties of Carex that occur on the USDA Beltsville Agricultural Research Center (BARC) in Maryland. One species (C. aquatilis Wahlenb) is new to the State of Maryland. The checklist is also compared to a checklist of vascular plants by Hotchkiss & Stewart (1948) from a nearby area—Patuxent Wildlife Research Center (PWRC); 12 species were not among our collections, while 8 species and 1 variety were found on BARC but not reported on PWRC.

Introduction

As part of a major sustainable agricultural initiative by the United States Department of Agriculture (USDA), the Agricultural Research Service (ARS) has been assessing insect biodiversity on the Beltsville Agricultural Research Center (BARC). This study area is the USDA Beltsville Agricultural Research Center (BARC) in Maryland, located between the Washington District of Columbia and Baltimore. It encompasses ~ 6,866 acres of which 3,074 acres is mixed pine and hardwood forests (Terrell et al. 2000), similar to what has been described in Hotchkiss & Stewart (1948) for the nearby Patuxent Wildlife Research Center (PWRC). The remainder is either maintained as open pastures and hayfields (25%), or utilized for cultivation of various crops (25%) and building complexes (2-3%). The open pastures include nearly 700 acres of “lawn” of which 10% is being redeveloped into “meadows”--lawns that have been plowed and seeded with various native herbs and grasses.

The genus Carex is of special interest because of a large variety of phytophagous insects that are associated with its species (Whitcomb unpublished), and also because of its taxonomic complexity and relatively large number of species of the BARC flora (Terrell et al. 2000). Among the insect feeders on Carex, species of leafhopper (Flexhamia) appear host specific. They are often found when species of Carex are sterile.

More than 500 specimens of Carex were collected during 1995-96 from various plant communities on BARC, primarily by Robert Whitcomb. Additionally, the senior author also collected ~30 specimens during the 1980's for Daniel Norris' taxonomic study of leaf anatomical characters, and 25 specimens during 1993 and 1994 for the sustainable agriculture initiative, and a similar number again in 1997.

Spjut, as an employee of the ARS, identified the collections obtained during 1993-1996. Harriman also compared the identifications to material at Oshkosh (OSH) where a large collection of Carex annotated by Jim Zimmerman is maintained. An additional ~100 specimens has since been collected by James Reveal, Matthew Cimino (Univ. Maryland), Edward Terrell with John Wiersema, and Richard Spjut. This material was also identified by Spjut as a contribution of World Botanical Associates (WBA), and  included one additional species not previously reported, C. canescens. Vouchers are deposited at OSH, the University of Maryland (MARY), the Botanical Research Institute of Texas (BRIT), and a single representative specimen of each species is retained at WBA.

A total of 44 species, and 4 varieties were identified; one species, C. aquatilis, is new to the state of Maryland. A key to 43 of the species is presented (C. canescens, a recent addition to the list, to be later added to the key). It is based on characters in taxonomic keys and descriptions in Brown and Brown (1984), Gleason (1952), Gleason and Cronquist (1991), Godfrey and Wooton (1979), Radford (1968), and also from Spjut's observations on other characteristics not mentioned in this literature. Kartesz (1994) was consulted to decide between differences of opinion. Generally, species status was followed when character differences were evident for perigynia features such as shape, whereas varietal status was followed if differences were based on vegetative features, or differences in length such as with anthers in C. virescens. Types were not consulted.

The species names are also listed alphabetically followed by notes on areas where collected on BARC, months when collected, and taxonomic problems. B/W refers to the Baltimore/Washington Parkway, NAL is the National Agricultural Library, and SCS is the acronym for Soil Conservation Service. The months of collection are not necessarily indicative of phenology, especially species represented by few collections. In other cases, this may include specimens collected in early flower and in late fruit. The most frequently collected species was C. virescens var. swanii, represented by 74 specimens; this is followed by C. annectans (46 specimens), C. lurida (41 specimens), C. festuacea (33 specimens), C. crinita (14 specimens),  C. debilis (14 specimens), C. atlantica var. capillacea (13 specimens), C. complanata var. hirsuta (13 specimens), C. intumescens (13 specimens), C. stipata (12 specimens), C. vulpinoidea (12 specimens), C. scoparia (11 specimens), and C. tribuloides (two vars., 18 specimens). Other less frequently collected species were observed to occur abundantly at their collection sites; these include: C. folliculata, C. frankii,  C. seorsa, and C. torta.

For comparative purposes we also note whether the species was reported on the nearby Patuxent Wildlife Research Center (PWRC) (Hotchkiss & Stewart 1948), an area predominantly of wetland forest (~80%) on 2,700 acres. Twelve species on that list, which have not yet been collected in our study area, are listed separately. Similarly noted are eight species and one variety found on BARC but not on PWRC.

Key to Carex spp. on BARC

1.  Perigynia without a distinct neck, shaped like a football.......... 2
1.  Perigynia with a distinct neck, shaped like a bottle.............. 13

2.  Spikes inconspicuous among basal leaves, on culms greatly 
      exceeded by basal leaves............................. C. abscondita
2.  Spikes on long culms, or on culms with reduced leaves.............. 3

3.  Perigynia irregularly swollen below apex, or contorted near apex... 4
3.  Perigynia symmetrical, not bent near apex.......................... 8

4   Leaves glaucous, 6-10 mm wide; staminate and pistillate spikes
      predominantly on separate culms with the dominant pistillate 
      spikes surpassed by a short peduncled, mostly sterile
      staminate spike and the dominant staminate spike greatly 
      surpassed by the mostly sterile pistillate spike..... C. laxiculmis
4.  Leaves dark green, 2-10 mm wide; pistillate and staminate
      spikes similar on all culms...................................... 5

5.  Scales acute to acuminate, sometimes shortly apiculate............. 6
5.  Scales with an excurrent awn from an obtuse to nearly truncate 
      apex............................................................. 7

6.  Leaves mostly 2-4 mm wide, numerous at base of plant; perigynia
      abruptly curved near apex; scales not gland dotted on mid
      nerve................................................. C. digitalis
6.  Leaves mostly 5-8 mm wide, more conspicuous on culms; pergyynia
      only slightly twisted near apex, with irregular bulges to near
      base; scales with numerous reddish glandular dots on midrib
      from base to apex, not in distinct rows.............. C. styloflexa

7.  Culm of staminate spike exceeding pistillate spike; 
      pistillate scales with a row of dotted glands on each
      side of midrib above the mid region, conspicuously
      ruffled near apex of lamina........................ C. gracilescens
7.  Culm of staminate spike not exceeding pistillate spike;
      pistillate scales lacking dotted glands, slightly
      wrinkled and fringed near apex of lamina................. C. blanda

8.  Leaves glaucous, without hairs except for being scabrous along
      margins; perygynia glabrous........................ C. flaccosperma
8.  Leaves and/or perygynia covered with short to long villous hairs, 
      occasionally only pubsecent on the sheath........................ 9

9.  Perigynia glabrous................................................ 10
9.  Perigynia pubescent............................................... 11

10. Leaf blades glabrous, pubescent on the sheath..................
     ...................................... C. complanata var. complanata
10. Leaf blades with curly white hairs, pubescent or glabrous on the 
      sheath.................................. C. complanata var. hirsuta

11. Scales with reddish-brown to purplish streaks on each side
      of midrib....................................................... 11B
11. Scales white to hyaline with green midrib, not streaked..........  12

11B. Inflorescences exceeding leaves by 1.5 to 2.0 times its length; 
       plants stoloniferous or rhizomatous............... C. pensylvanica
11B. Infloresences slightly exceeding leaves; not spreading by
       stolons, the culms produced in clumps at base......... C. albicans

12. Anthers 1.5-2.5 mm long.................. C. virescens var. virescens
12. Anthers 0.5-1.5 mm long..................... C. virescens var. swanii

13. Perigynia flat, scalelike, similar in texture, color and shape 
     to scales........................................................ 14
13. Perigynia turgid to inflated, easily distinguished from scales
     (Note: immature forms of Carex typhina resemble C. synchocephala
     and will key to the above; however, spikes are gynandrous and 
     perigynia have 3 stigmas)........................................ 22

14. Perignia lanceolate, with a neck longer than body................. 15
14. Perignia ovate, with a neck shorter than body..................... 18

15. Bract subtending flower head with a narrow green midrib; leaves
     relatively narrow, 1-2.5 mm wide, dirty green; flower heads
     ellipsoidal and acuminate when young, ovoid and acute at 
     maturity................................................ C. scoparia
15. Bract subtending flower head with a dilated green midrib bordered
     by a hyaline sheath, tightly clasping the spike; leaves 3-5 mm 
     wide, dark green and somewhat flaccid, or yellowish-green and 
     stiff; flower heads ellipsoidal when young (similar to
     C. muskingumensis), cylindrical and truncate to obtuse at
     maturity......................................................... 16

16. Perigynia brown and nerved over the achene, cf. illus. in
     Radford................................................. C. normalis
16. Perigynia white and nerveless to faintly nerved over achene,
     white fringed along margins; cf. New Gleason and Cronquist....... 17

17. Leaves dark green, flaccid............... C. tribuloides var. rudecta
17. Leaves yellowish-green, stiff (cf. key in Radford).....C. tribuloides

18. Persistent male scales tinted brown, closely imbricate, in
      a series longer than the female series above, cf. illus in
      Gleason's Britton & Brown............................. C. straminea
18. Persistent male scales hyaline with green nerves, loosely
      imbricate, in a series shorter than female series............... 19

19. Perigynia rounded to apex, nerveless; scales nearly equal to 
      perygynium in length, short awned; immature plants of..........
      ................................................... C. cephalophora
19. Perigynia abruptly contracted or incurved on upper body, 
      5-7 nerved over the achene; scales ca. 3/4 length of perygynium, 
      acute, acuminate to slightly awned.............................. 20

20. Scales reaching midway or more into the neck of the perigynium;
      heads mostly aggregate............................ C. albolutescens
20. Scales barely reaching the neck of perigynium; heads mostly 
      scattered....................................................... 21

21. Perigynia abruptly contracted and folded on shoulder margin of
      upper body, bristly along margins below neck, becoming less 
      bristly on neck towards apex, 5-nerved over the achene,
      plicate around body of achene; scales acuminate to slightly
      awned with a concave to recurved acumen; styles not persistent..
      ..................................................... C. festucacea
21. Perigynia mostly plane to slightly wrinkeld on upper margins of
      body, bristly margined to apex, 7-nerved over achene, 
      wrinkled in net-like manner around body of achene; scales 
      obtuse to acute, mostly plane; styles persistent... C. hormanthodes

22. Perigynia turgid; male flowers above or below female flowers in
      same spikes..................................................... 23
22. Perigynia inflated; male flowers in separate spikes............... 35

23. Leaf sheaths transversely wrinkled or rugose...................... 24
23. Leaf sheaths not transversely wrinkled............................ 26

24. Outer face of perigynia finely nerved with 5 or more nerves more
      or less equally spaced across the entire width of perygynium,
      at least below the mid region, nerveless on inner face;
      scale about half to three-fourths the length of the perygynium,
      with short excurrent midrib, or acuminate............... C. stipata
24. Nerves of perygynia evident only in mid region, 3-4 nerved; scale 
      nearly equal to or longer than the perygynium in length, with
      awn about as long to longer than the lamina part................ 25

25. Neck of perygynia entire, or with scattered minute bristles
      (difficult to see at 30x), relatively long, ca. 1 mm long;
      basal bract of spike exceeding the length of spike in 
      fruit............................................... C. vulpinoidea
25. Perigynia densely bristly margined on neck and upper body; neck
     of perigynia relatively short, ca. 0.5 mm long; basal
     bract of spike about equal to length of spike.......... C. annectens

26. Spikes continuous, generally aggregate near apex.................. 27
26. Spikes scattered along culms, sometimes crowded near apex but
      not continuous.................................................. 29

27. Perigynia ovate, nerveless or 3-nerved on outer face in the mid
      region; inflorescence capitulate near apex of culm.............. 28
27. Perigynia lanceolate, gradually tapering to a long slender neck, 
      with nerves extending to apex on back, to midregion on inner 
      face; aggregate of spikes linear along culm....... C. laevivaginata

28. Perigynia deflated, mostly entire along upper margins and neck;
      scales mostly not awned; plants slender with culms under 20 cm 
      in length................................................ C. divisa
28. Perigynia turgid, bristly along upper margins and neck;
      scales awned; culms 40 cm or more in length........ C. cephalophora

29. Perigynia pregnant below mid region, plane on the inner 
      face with incurved margins, convex on the outer face; male 
      flowers borne above female flowers.............................. 30
29. Perigynia pregnant near apex, inner face concave below, convex 
      above, outer face convex, margins not incurved but with thick 
      nerve; male flowers borne below female flowers.................. 32

30. Perigynia smooth along upper margins; scales falling before 
      perigynia............................................ C. retroflexa
30. Perigynia serrulate above; scales persistent or deciduous......... 31

31. Inner face of perigynia with 4-8 conpicuous intermarginal 
      nerves over the inflated (spongy-thickened) region, nerveless
      above; pistillate scales soon deciduous, hyaline with green
      midnerve; cf. 2nd ed. Gleason & Cronquist............... C. radiata
31. Inner face of perigynia more wrinkled than nerved, or nerveless;
      pistillate scales persistent, hyaline and tinged golden brown
      along green midnerve...................................... C. rosea

32. Perigynia prominently nerved on inner face with most nerves
      extending to near apex, densely bristly margined on neck...
      ..................................................... C. incomperta
32. Perigynia with most nerves on inner face fading near mid region,
      or nerveless; neck entire to bristly............................ 33

33. Neck of perigynia short, not minutely bristly margined, with
      9-10 minute punctate glands near margins (barely visible
      at 30x); leaves flat, broad.............................. C. seorsa
33. Neck of perygnia short to long, sparsely to closely bristly along 
      margins, not minutely glandular punctate; leaves flat to 
      inrolled........................................................ 34

34. Terminal spike separated from next lower spike by 2 (-3) 
      scattered male florets; spikes with ca. 5-8 perygynia, 
      1-3 mm wide and long; perigynia 2.0-2.2 (-2.5) mm long, 
      imbricate, spreading in various directions at maturity, 
      the upper often erect, lower reflexed; leaves flaccid, or 
      flexuous, ca. 1 mm wide............... C. atlantica var. capillacea
34. Terminal spike separated from next lower spike by 4 (-6) 
      scattered male florets; heads with ca. 7-11 perygynia, 4-5 mm wide 
      and long; pergynia 2.5-3.0 mm long, all in more or less vertical
      ranks, equally divergent, perpendicular to axis; leaves turgid,
      1-2 mm wide............................ C. atlantica var. atlantica

35. Perigynia loosely overlapping each other along rachis, fusiform....
      ........................................................ C. debilis
35. Perigynia aggregate in cylindrical to distichous spikes, 
      generally vaselike.............................................. 36

36. Scales with reddish-brown bands on each side of mid-rib........... 37
36. Scales green or green with hyaline margins........................ 39

37. Leaf sheaths fimbriose; spikes erect; perigynia rounded
      at apex, not twisted, slightly or not recurved.......... C. stricta
37. Leaf sheaths not fimbriose; spikes curved; perigynia tapering 
      to apex, twisted or recurved near apex.......................... 38

38. Leaves pleated, toothed along upper nerves and margins..... C. torta
38. Leaves deeply folded along upper midrib and inrolled near margins,
      entire................................................ C. aquatilis

39. Perigynia only slightly inflated, not exceeding 4 mm; pistillate
      spikes narrow linear, often 10 times or more longer than wide;
      scales with an excurrent serrulate awn.................. C. crinita
39. Perigynia much inflated, exceeding 4 mm; pistillate spikes broad
      linear to globose, usually not more than 5 times longer than wide;
      scales with or without an excurrent serrulate awn............... 40

40. Perigynia relatively large, 10-20 mm long, loosely aggregate and
      often spreading in various directions near apex; scales ovate-
      lanceolate, mostly acute........................................ 41
40. Perigynia relatively small, less than 10 mm long, tightly congested
      in cylindrical heads; scales generally narrow, oblong, or 
      lanceoleate to linear, often awned.............................. 44

41. Perigynia 3-15 in short spikes.................................... 42
41. Perigynia more than 15 in elongated spikes........................ 43

42. Perygynia distichous.................................. C. folliculata
42. Perigynia radially arranged in subglobose heads....... C. intumescens

43. Pergynia 13-20 mm long, leaves 6-10 mm wide.............. C. lupulina
43. Pergynia 8-13 mm long, leaves 3-6 mm wide............. C. louisianica

44. Scales with subulate serrulate awns longer than the perigynia....
     ......................................................... C. frankii
44. Scales mostly inconspicuous, shorter than perigynia, membranous
      with or without excurrent awn................................... 45

45. Pistillae scales sheathlike, cuspidate, with serrulate awn as long
      as the sheath............................................ C. lurida
45. Pistillae scales tapered to apex without an excurrent awn, or 
      midrib shortly excurrent........................................ 46

46. Pistillate scales oblong or broadly linear, acute......... C. typhina
46. Pistillate scales acute or acuminate with a short excurrent
     awn.................................................... C. squarrosa

                       List of Carex spp. and Notes

C. abscondita Mack.  Occasional (5 specimens): rich forests, especially
        towards margins, Indian Creek, Beaver Creek; May 29-Jun 15.  
C. albicans Willd. ex Spreng. Rare: (2 specimens): margin of 
        chestnut oak-pine forest, Springfield Road, Poultry Road pasture.
        This may prove to be C. pensylvanica. The differences 
        in perigynial shape mentioned in the literature seem minor.
C. albolutescens Schwein. Occasional (5 specimens): edge of woods.
C. annectens (E. P. Bicknell) E. P. Bicknell (C. vulpinoidea 
        Michx. var. ambigua. Common (46 specimens): mostly sunny 
        moist places�ditches, meadows; May 22-Jul 18. 
C. aquatilis Wahlenb. Infrequent (2 specimens): fresh water marsh in 
        roadside slough, W of Soil Conservation Service Road between 
        road and artificial pond, with other sedges and Andropgon 
        glomeratus; May 29. New to Maryland. 
C. atlantica Bailey. Occasional (6 specimens): Sphagnum bogs 
        bordering forest and lakes; Beck Lake, south shore; May 29-Jun 1. 
C. atlantica var. capillacea (L. Bailey) Reznicek (C. 
        howei Mack.). Locally common (13 specimens): Sphagnum bogs 
        along shores of ponds or lakes, margins of wet powerline cuts
        through forested areas; dominant along south shore of Beck Lake;
        May 29-Jun 15. This is considered a distinct species (C. howei
        Mack.) in Brown & Brown (1984), a variety in Gleason and 
        Cronquist, or a subspecies in Kartesz.  The leaves are the 
        narrowest of a sedge complex that includes var. atlantica, 
        C. incomperta, and C. seorsa in which the leaves 
        become progressively broader in the order indicated. 
C. blanda Dewey. Occasional (3 specimens): pastures and powerline 
        cuts, May 25-31.
C. canescens L., rare in open shrub swamps (1 specimen).
C. cephalophora Muhl. ex Willd (Includes C. mesochorea).
        Infrequent (7 specimens): meadows and pastures, May 11-Jun 25.  
        Appearing variable in length and thickness of infloresence and
        perigynia.  Two specimens have perigynia ca. 3.5 mm long, 
        another ca. 3.0 mm. Immature specimens may key to C. alata.  
        Carex leavenworthii Dewey is similar and reported from one 
        location on PWRC. 
C. complanata Torr. & Hook. Infrequent (2 specimens): woods and
        meadows along powerline cut-through, and oak barren north glade 
        meadow, BARC and PWRC; May 29.
C. complanata var. hirsuta (Bailey) Gleason. Common (13 specimens): 
        Powerline cuts through coniferous, wet meadows, May 22-Jun 21.
C. crinita Lam. Locally common (14 specimens): sunny wet places near 
        water, or in standing water, cleared areas; May 29-Jun 19 (-Aug 18).
C. debilis Michx. Frequent (14 specimens): floodplain forests, 
        meadows, along paths, May 29-Jun 21. 
C. digitalis Willd. Occasional (3 specimens): Entomology road pond
        in damp woods near fence, Lower Beaver Dam Creek flood-plain behind 
        old wastewater treatment plant in drier woods near margin of forest; 
        BARC and PWRC; Jun 8-13.
C. divisa Huds. Rare (1 specimen): pasture, unseeded, Poulty Road, 
        BARC; May 15.
C. festucacea Schkuhr ex Willd. Common (33 specimens): Wet 
        places at forest edges; May 29-Jun 21.  Most specimens have 
        perigynia ca. 2 mm wide. Several have perigynia ca. 2.5 mm wide, 
        which are also more widely divergent in the inflorescence; these 
        might be referred to C. bicknellii or C. cristatella. 
C. flaccosperma Dewey. Common (19 specimens): meadows, forest 
        margins, May 6-Jun 14. Includes C. glauca. 
C. folliculata L. Common (4 specimens): Sphagnum bogs, 
        powerlines, seepages in forests, swampy lake shores; BARC and PWRC; 
        May 29-Jun 19.
C. frankii Kunth. Common (9 specimens): floodplain forests, wet 
        ditches in pastures; Jun 8-Jul 10.
C. gracilescens Steudel. Occasional (2 specimens): oak pasture 
        near oak-hickory-pine forest with dense huckleberry understory, 
        Beaver Dam Creek, BARC; May 14-24. 
C. hormanthodes Fernald. Occasional (5 specimens): Edges of wet 
        forest, Beck Lake, Entomology Road, airport; BARC and PWRC; 
        May 24-29.  Very similar to C. festucacea, distinguished 
        also by the relatively shorter and more inflated epidermal cells 
        of the perigynia where it covers the achene. 
C. incomperta E. P. Bicknell. Occasional (3 specimens): bogs along 
        powerline cuts through forest (�Deciduous Research Forest 
        Powerline�), mesic site with bracken fern, or with Leersia, 
        or with Sphagnum, BARC and PWRC; May 29-Jun 1. Included under
        C. atlantica by Gleason & Cronquist (1991). The key character 
        in Brown & Brown (1984) for distinguishing C.incomperta from
        C. atlantica is the perigynium having a sharply notched apex 
        in the former vs. only slightly notched apex in the latter. This 
        appears insignificant.  On the other hand, the prominent nerves
        on the inner face of the perigynia seems diagnostic, and apparently 
        correlates with the key character of coarse stems indicated 
        in Brown & Brown (1984).  Additionally, the male flowers below the 
        terminal spike overlap more closely than in C. atlantica.
C. intumescens Rudge. (Common): 13 specimens; woods and powerlines;
        BARC and PWRC; May 29-Jun 21. 
C. laxiculmis Schwein. Occasional (3 specimens): Beaver Dam Creek 
        floodplain behind old wastewater treatment plant; drier woods 
        near margin of forest in rich soil and full shade; BARC and 
        PWR; Jun 13-15. 
C. laevivaginata (K�k.) Mack. Occasional (4 specimens): Standing 
        water, streams or bogs in forest; Research Road, Entomology Road; 
        BARC and PWRC; May 29-Jun 13.
C. louisianica Bailey. Occasional (3 specimens): bogs; Beck 
        Lake, airport; BARC and PWRC; Jun 19.
C. lupulina Muhl. ex Willd. Occasional (4 specimens): 
        open sunny marsh, Beaver Dam Creek, BAARC and PWRC; Jun 8-21. 
C. lurida Wahlenb. Common (41 specimens): open wet sunny places; 
        marshes, ditches, streams, powerlines, meadows; May 19-Jul 10.  
        Includes C. baileyi.
C. normalis Mack. Rare (1 specimen): floodplain forest, Beaver Dam
        Creek.
C. pensylvanica Lam. Clonal plants numerous, but occurring locally
        among ferns in understory of mixed conifer hardwood forest east 
        of Beck Lake (1 specimen), Mar.
C. radiata (Wahlenb.) Small. Frequent (7 specimens): floodplain 
        in forests, May 30-Jun 15.  This is C. rosea in Brown and 
        Brown (1984).
C. retroflexa Muhl. ex Willd. Rare (1 specimen): mesic woods 
        between stream and forest margins, Poultry Road, May 23.
C. rosea Schkuhr ex Willd. (Includes C. convoluta 
        Mack.). Occasional (4 specimens): lower Beaver Dam Creek flood-plain
        behind old wasterwater treatment plant, Poultry Road; BARC and PWRC; 
        May 14. 
C. scoparia Schkuhr. Common (11 specimens): in marsh communities that
        developed from forest clearing, with dominant Leersia oryzoides, 
        or with Andropogon glomeratus, also roadside ditches, stream 
        borders in meadows, or along powerline cuts; May 16-Aug 2.  
        Variable in shape of inflorescence, some specimens approach 
        C. muskingumensis in spikes being scattered and ellipsoidal, 
        while others with a more  capitate inflorescence approach 
        C. crawfordii Fernald.  Perigynia are mostly 5.0 mm long 
        and nearly 2.0 mm wide.
C. seorsa Howe. Common (6 specimens): Seepages among vegetation 
        in woods, South farm, Beaver Dam Creek, airport; BARC and PWRC; 
        May 31-Jun 21.
C. squarrosa L. Occasional (6 specimens): pastures and floodplain 
        forests, BARC and PWRC; Jun 8-23.
C. stipata Muhl. ex Willd. Frequent (12 specimens): powerline 
        cuts, floodplain forest; Beaver Dam Creek, B/W Parkway, Beltway;
        BARC and PWRC; May 21-Jun 14. 
C. straminea Willd. ex Schkuhr. Rare (1 specimen): oak barren 
        pasture, BARC.
C. stricta Lam.; Infrequent (2 specimens): Sphagnum bog along 
        powerline, coniferous forest, BARC and PWRC; Jun 1.
C. styloflexa Buckley. Rare (1 specimen): Lower Beaver Dam woods, 
        BARC; date of collection uncertain. 
C. torta Boott ex Tuckerman.  Common (2 specimens): Beck 
        Lake, south shore, mixed sedge community, BARC; May 29. 
C. tribuloides Wahlenb. var. tribuloides Frequent (9 specimens): 
        open places near edges of water, floodplain soils, powerlines; 
        Beaver Dam Creek, Indian Creek, Olla wet meadow, Oak Barren North 
        Glade, airport; BARC and PWRC; Jun 13-14. Four other specimens 
        from open sunny fields with either rush and Leersia, or 
        with sedge fern communities, collected earlier in the season, 
        May 29-30, closely resemble C. muskingumensis Schwein.; 
        however, the perigynia are all about one-half the size reported 
        for that species, thus, they would seem to be an immature form 
        of C. tribuloides.
C. tribuloides var. reducta Gray (C. projecta Mack.).
        Frequent (9 specimens): in standing water or wet meadows, Beaver 
        Dam Creek flood-plain, BARC; May 31-Aug 2. Appears to differ from 
        the typical variety only by leaf characters as outlined in Radford, 
        possibly a shade tolerant variety. 
C. typhina Michx. Occasional (9 specimens): floodplain forests and 
        oak pasture, BARC and PWRC; May 23-Jun 23. 
C. virescens Muhl. ex Willd; only one specimen (immature) 
        was interpreted as typical of the species (anthers ca. 2 mm 
        long), see below; on PWRC also reported in one station, margin 
        of terrace forest.
C. virescens var. swanii (Muh. ex Willd.) Fern. Common
        (74 specimens): many habitats, distinguished from the typical 
        variety by size of anthers; May 4-Aug 2.  This is usually treated 
        as a distinct species, but differences seem minor.
C. vulpinoidea Michx. Common (12 specimens): wet fields or pasture, 
        Poultry Road, Entomology Road, B/W Parkway, airport, Beltway, 
        BARC and PWRC; May 30-Jun 29. 

Species Reported on Patuxent Wildlife Research Center (PWRC) not listed 
above.

C. aggregata Mackenzie.  One record in abandoned field.
C. amphiloba Steudel (C. grisea Wahlenb.).  Rare in bottomland forest.
C. caroliniana Swein.  Occasional in wood margins on flood plant and 
       terrace.
C. grayi Carey.  One station in bottomland forest.
C. lacustris Willd.  One station along margin of shrub swamp.
C. leavenworthii Dewey.  One station in lawn.
C. longii Mackenzie.  Occasional in wet meadows.
C. lupuliformis Sartwell & Dewey.  One station in run in river swamp.
C. tonsa (Fern.) Bickn.  Occasional in sandy wood margins on upland.
C. umbellata Schkuhr. ex Willd. One station in open terrace forest.
C. venusta Dewey (C. oblita Steudel). One station in seepage swamp.
C. willdenowii Schkuhr. ex Willd.  Rare in terrace forest and wood 
       margins.

Species and Varieties Reported on BARC and not PWRC

C. aquatilis
C. atlantica var. atlantica.
C. divisa 
C. gracilescens
C. normalis
C. straminea
C. styloflexa
C. tribuloides var. rudecta
C. torta

                             Literature Cited

Brown, M. L. and R. G. Brown. 1984.  Herbaceous plants of Maryland. 
    Port City Press, Baltimore.

Gleason, H. A. and A. Cronquist.  1991.  Manual of vascular plants of 
    northeastern United Stated and adjacent Canada.  Second Edition.  The 
    New York Botanical Garden, New York. 

Gleason, H. A.  1952.  Illustrated flora of the northeastern United 
    States and adjacent Canada.  Vol 1. Lancaster Press, Lancaster.

Godfrey, R. K. and J. W. Wooton.  1979.  Aquatic and wetland plants of 
    southeastern United States.  University of Georgia Press, Athens.

Hotchkiss, N. & R. E. Stewart.  1948.  Vegetation of the Patuxent Research 
    Refuge, Maryland. Amer. Midland Nat. 38: 1-75.

Kartesz, J. T. 1994.  A synonymized checklist of the vascular flora of the 
    United States, Canada, and Greenland.  Timber Press, Portland.

Radford, A. E., H. E. Ahles and C. Ritchie Bell.  1968.  Manual of the 
    vascular flora of the Carolinas.  University of North Carolina Press, 
    Chapel Hill.

Terrell, E. E., J. L. Reveal, R. W. Spjut, R. F. Whitcomb, J. H. Kirkbride, 
    Jr., M. T. Cimino and M. Strong.  2000.  Annotated list of the flora of the 
    Beltsville Agricultural Research Center, Beltsville, Maryland. 
    USDA ARS-155, Natl. Tech. Info. Serv., Springfield, VA.

Acknowledgments

Assistance is gratefully appreciated from Neil Harriman, Biology Department, University of Wisconsin�Oshkosh, WI 54901 for identifications, and review of the manuscript. This work was largely supported by the Agricultural Research Service in Beltsville, Maryland.

^{1 World Botanical Associates moved from Laurel Maryland to Temecula California in Oct 2001, and then
     to Bakersfield California in Aug 2004}

^{2. Dr. Robert Whitcomb retired from the USDA Agricultural Research in 1997}