Research Article |
Corresponding author: Peter W. Schafran ( pscha005@odu.edu ) Academic editor: Pavel Stoev
© 2016 Peter W. Schafran, Steven W. Leonard, Rebecca D. Bray, W. Carl Taylor, Lytton J. Musselman.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Schafran PW, Leonard SW, Bray RD, Taylor WC, Musselman LJ (2016) Isoetes mississippiensis: A new quillwort from Mississippi, USA. PhytoKeys 74: 97-106. https://doi.org/10.3897/phytokeys.74.10380
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Isoetes mississippiensis S.W. Leonard, W.C. Taylor, L.J. Musselman and R.D. Bray (Isoetaceae, Lycopodiophyta) is a new species known from two sites along tributaries of the Pearl River in southern Mississippi. This species is distinguished from other species in the southeastern United States by a combination of character states including a basic diploid (2n=22) chromosome count, laevigate megaspores, and a narrow velum covering less than one-third of the adaxial sporangium wall.
Isoetes , Isoetaceae , lycophyte, quillwort, Mississippi
Isoetes (Isoetaceae) is a cosmopolitan genus of heterosporous lycophytes containing 200–300 species (
In spite of their antiquity, widespread distribution, and diverse ecological adaptations, Isoetes species are remarkably uniform in their morphology. Plants appear simple in form with a lobed subterranean rootstock producing a tuft of linear sporophylls above and below roots along a groove between the lobes. This apparent morphological simplicity makes it easy to recognize a member of the genus, but difficult to distinguish species. Earlier taxonomists relied primarily on habitat, megaspore texture, and megaspore size to separate taxa (
Ornamentation and size of megaspores and microspores are important morphological features used to identify species of Isoetes.
The habitat of species of Isoetes can be fairly specific and is often used in taxonomic treatments (
Characteristics of sporophylls and rootstocks of Isoetes may also provide taxonomic information, though the utility of some of these features is questionable. Velum coverage of the sporangium, sporangium shape, sporangium wall coloration, and sporophyll length, number, color, and shape are sometimes used for species identification, but these character states can be subtle and it is unclear how they may be influenced by environmental conditions (
While searching for populations of Isoetes louisianensis in southwestern Pearl River Co., MS, in the spring of 1996, one of us (Leonard) discovered a population of Isoetes that did not appear to be I. louisianensis or any other known species. These plants had very long and numerous sporophylls bearing megaspores with a smooth surface rather than an irregularly reticulate texture that is typical of I. louisianensis megaspores. In addition, the megaspores of this plant were noticeably smaller than those of I. louisianensis. Further investigation turned up a second population downstream in Lotts Creek. Both of these waterways are tributaries of the Pearl River, converging near Picayune, MS.
Field work was performed in 1996, 1998, and 2013 to obtain specimens for further study. Specimens were deposited in the Old Dominion University herbarium (
Analysis of morphological characters, chromosome counts, and ecological evaluation leads us to conclude our collections represent an undescribed species of Isoetes.
USA. Mississippi: Lotts Creek (30.57396°N, 89.76196°W, elevation 14 m), 18 June 2013, P. Schafran MS-08 L. Musselman, S. Leonard, W. Taylor, M. Alford, and D. McNair (holotype:
Plants amphibious in and along persistent streams. Rootstock subglobose, bilobed, brown, 0.5−1.0 cm long, 1.0−1.5 cm wide. Roots dichotomously branched. Sporophylls (leaves) linear, bright green, darkening with age, pale toward base, spirally arranged, erect to spreading, up to 40 cm long and 2.0 mm wide at mid-length, in tufts of ca. 20, semi−terete with adaxial surface flattened, becoming more terete distally, with translucent alae ca. 1 mm wide extending along lateral edges from base to ca. one-quarter leaf length, tapering gradually toward apex, abruptly dilated and spatulate toward base where streaks of brown pigmented cells are often evident on pale outer surface of leaf base. Ligule triangular, ca. 1 mm long. Sporangium ovate, most 4−10 mm long, most 4−5 mm wide, adaxial wall spotted to streaked with scattered clusters of brown pigmented cells. Velum incomplete, covering less than one third of sporangium wall. Megaspores globose, white, trilete, macro-ornamentation laevigate with echinate micro-ornamentation, ca. 280−380 µm in diameter, averaging ca. 340 µm. Microspores broadly fusiform, macro-ornamentation echinate with bacillate micro-ornamentation, pale brown in mass, monolete, 25−30 µm long.
Rootstocks of all specimens examined vary in length from 0.5−1.0 cm and in width from 1.0−1.5 cm. All rootstocks are subglobose in shape and bilobed. Sporophylls reach a maximum length of 40 cm and maximum width of 2.0 mm at mid-length. Sporangia are 4−10 mm long and 4−5 mm wide. Megaspores are laevigate with echinate micro-ornamentation (Figures
Chromosome counts show individuals of Isoetes mississippiensis to be diploid (2n=22).
Isoetes mississippiensis occurs in sluggish, persistent streams in southern Mississippi (Figure
After flowing west for several kilometers, Moody Branch turns sharply south just west of Mississippi Highway 43 and eventually merges with Lotts Creek. The forested wetland adds pond cypress (Taxodium ascendens) and a dense shrub understory with Smilax laurifolia. At the Walkiah Bluff Road crossing of Lotts Creek disturbance has been severe, yet I. mississippiensis has revegetated new habitat in the roadside ditch north of the road and on sandbars.
This species is named for the state of Mississippi, its only known locality.
Leonard 9393, 9 March 1996 (
Evaluation of the morphological and cytological features of I. mississippiensis shows it to be distinct from all other taxa in the southeastern US. In the coastal plain of the Gulf Coast states, nine other species are known: I. appalachiana, I. boomii, I. flaccidas.l., I. hyemalis, I. louisianensis, I. melanopodas.l., I. microvela, I. texana, and I. valida (
Character | I. mississippiensis | I. texana | I. flaccida s.l. | I. melanopoda s.l. | I. valida |
---|---|---|---|---|---|
Ploidy | 2n=22 | 2n=22 | 2n=22 | 2n=22 | 2n=22 |
Habitat | Persistent streams | Persistent freshwater ponds, interdunal swales | Springs, stream bottoms, river bottoms, ditches |
Ephemeral wet prairies, open graminoid swales, woodland pools, soil pockets on rock outcrops | Woodland seepages |
Megaspore Ornamentation | Laevigate | Smooth to obscurely rugulose | Low tubercules to broad, interconnected mounds | Low tubercles or ridges | Broken reticulate |
Megaspore Size (mm) | 280–380 (x=340) | 350–405 (no mean reported) | 250–500 (no mean reported) | 280–440 (x=380–410) | x=450 |
Microspore Ornamentation | Spinulose/echinate | Papillose | Papillose | Spinulose/echinate | Spinulose/echinate |
Microspore Size (mm) | 25–30 | 25–30 | 25–33 | 20–30 | 27 |
Velum Coverage (%) | 15–33 | 100 | 80–100 | 5–15 | 45–70 |
Character | I. louisianensis | I. hyemalis | I. appalachiana | I. boomii | I. microvela |
Ploidy | 2n=44 | 2n=44 | 2n=44 | 2n=66 | 2n=66 |
Habitat | Creeks, streams | Blackwater streams | Creek banks, woodland pools, lakes | Slow-flowing woodland streams | Persistent streams in deciduous swamp forests |
Megaspore Ornamentation | Irregularly reticulate | Broken reticulate to sub-echinate | Broken reticulate | Cristate to reticulate | Densely reticulate with irregular crests and thin tubercles |
Megaspore Size (mm) | 500–625 (no mean reported) | 400–580 (=522) | 450–611(=534) | 460–610 (no mean reported) | =527 |
Microspore Ornamentation | Spinulose/echinate | Spinulose/echinate | Psilate to low tuberculate | Papillose/aculeate | Psilate to low tuberculate |
Microspore Size (mm) | 25–35 | 20–31 | 29–32 | 25–30 | 30 |
Velum Coverage (%) | <50 | 10–20 | 20–25 | 30–50 | 10 |
1 | Megaspores psilate to laevigate, rarely low tuberculate or low rugulate | 2 |
2 | Plants at least sometimes with darkened, often sclerified, brown-black leaf bases; velum coverage generally <15% | I. melanopoda s.l. |
2' | Plants never with darkened leaf bases; velum coverage usually >15% | 3 |
3 | Megaspores 280-380 mm; velum coverage 15-30% | I. mississippiensis |
3' | Megaspores 350-405 mm; velum coverage 100% | I. texana |
1' | Megaspores tuberculate, reticulate, cristate, or rugulate | 4 |
4 | Velum coverage 75-100%; microspores papillose | I. flaccida s.l. |
4' | Velum coverage less than 75%; microspores echinate | 5 |
5 | Megaspore ornamentation of tubercles or ridges; velum coverage less than ca. 25% | I. melanopoda s.l. |
5' | Megaspore ornamentation broken reticulate; velum coverage between ca. 25 and 75% | I. valida |
Isoetes mississippiensis is known from only two locations along approximately 2 miles of the Lotts Creek—Moody Branch waterway. Neither of these populations is located on preserved land. Extensive field work is needed to search for additional populations in the nearby Pearl River Wildlife Management Area and Bogue Chitto National Wildlife Refuge.
The authors wish to thank Mac Alford and Daniel McNair (University of Southern Mississippi) for their assistance in the field. Funding was provided by the Mary Payne Hogan endowment at Old Dominion University. Scott Whittaker and Liz Zimmer (National Museum of Natural History, Smithsonian Institution) helped generate scanning electron micrographs. We are grateful for the comments of two anonymous reviewers.