Isoetes mississippiensis S.W. Leonard, W.C. Taylor, L.J. Musselman & R.D. Bray, 2016

Schafran, Peter W., Leonard, Steven W., Bray, Rebecca D., Taylor, W. Carl & Musselman, Lytton J., 2016, Isoetes mississippiensis: A new quillwort from Mississippi, USA, PhytoKeys 74, pp. 97-106 : 99-101

Isoetes mississippiensis S.W. Leonard, W.C. Taylor, L.J. Musselman & R.D. Bray sp. nov.

Type.

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: US; isotypes: MO, NY, ODU, USMS).

Description.

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.

Morphology.

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 1 , 2 , 3 ). Diameter of megaspores varies from 280-380 µm, with an average of 340 µm. Microspores are echinate with bacillate micro-ornamentation, and are 25-30 µm long (Figure 1 ).

Cytology.

Chromosome counts show individuals of Isoetes mississippiensis to be diploid (2n=22).

Ecology.

Isoetes mississippiensis occurs in sluggish, persistent streams in southern Mississippi (Figure 4 ). At the Moody Branch locality, the maintained right-of-way of Mississippi Highway 43 allows abundant sunshine to reach the stream and adjacent wetlands. Small bushes and saplings of titi ( Cyrilla racemiflora ) and red maple ( Acer rubrum ) are periodically cut down and allowed to fall in the stream. Sediment and detritus provide anchors for herbaceous growth of sedges, rushes, and coarse grasses ( Rhynchospora inexpansa , Juncus spp., Erianthus giganteus , Panicum spp.). In the shallow water stream margin is Iris virginica . The woodland edge is suitable habitat for crossvine ( Bignonia capreolata ) and rattan vine ( Berchemia scandens ). Upstream where a defined channel is present the overstory consists of swamp black gum ( Nyssa biflora ), laurel oak ( Quercus laurifolia ), red maple, and encroaching loblolly pines ( Pinus taeda ). Shrubs in the understory are Elliott’s blueberry ( Vaccinium elliottii ), yaupon ( Ilex vomitoria ), and titi. In the upper reaches of Moody Branch, the channel is braided and the water sluggish, more typical of a swamp black gum forest with Rankin’s jessamine ( Gelsemium rankinii ), Virginia willow ( Itea virginica ), and dog hobble ( Viburnum nudum ).

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 Isoetes mississippiensis has revegetated new habitat in the roadside ditch north of the road and on sandbars.

Etymology.

This species is named for the state of Mississippi, its only known locality.

Specimens examined.

Leonard 9393, 9 March 1996 (MMNS); Leonard 9395, 22 March 1996 (MMNS); Leonard 9831, 2 June 1997 (MMNS); Leonard 12405, 12 May 2011 (ODU); Leonard 12406, 12 May 2011 (ODU); Musselman with Taylor, 98908, 17 October 1998 (ODU); Bolin JB-MS-01, 9 January 2009 (ODU); Schafran MS- 07, 18 June 2013 with Musselman, Leonard, Taylor, and Alford (MO; NY; ODU; USMS); Schafran MS-08, 18 June 2013 with Musselman, Leonard, Taylor, and Alford ( US; ODU); Taylor 6798, 18 June 2013 with Musselman , Leonard , Schafran, and Alford ( US) .

Figures

Figure 1. SEMs of megaspores (a, b, c) and microspores (d, e, f) of Isoetes mississippiensis displaying distal (a, d), equatorial (b, e), and proximal (c, f) views. Megaspores from Schafran MS- 08, microspores from Taylor 6798. Megaspore magnification 200 x; microspore magnification 2000 x.

Figure 2. SEM detail of megaspore micro-ornamentation. Magnification 2000 x.

Figure 3. Light microscope image of megaspores of Isoetes mississippiensis from Schafran MS- 07 (left) and MS- 08 (right). Magnification 63 x. Scale bar = 0.3 mm.

Figure 4. Map showing two localities of Isoetes mississippiensis. Inset: Map of Mississippi with detail area highlighted. Map created using ArcGIS software (Esri).