Isoetes dubsii J.B.S.Pereira, 2019

Pereira, Jovani B. de S., Guimaraes, Jose Tasso F. & Watanabe, Mauricio T. C., 2019, Isoetes dubsii and Isoetes santacruzensis, two new species from lowland areas in South America, PhytoKeys 131, pp. 57-67 : 57

Isoetes dubsii J.B.S.Pereira sp. nov. Figs 1 , 2

Diagnosis.

Isoetes dubsii is distinguished from other species from the Brazilian Pantanal wetlands by a set of characters that include leaves that are long (90-100 cm), flexuous and trigonal in the transverse section, tri-lobated stems, rudimentary velum, pustulate and small megaspores of 310-390 µm in diameter (average 350 µm) and laesurae of the megaspore at least four times wider than high.

Type.

BRAZIL. Mato Grosso do Sul: Fazenda Salina, Pantanal do Rio Negro, 19°30'S, 56°10'W, 3 Jun 1988, Dubs 829 (holotype: Z!).

Description.

Plants aquatic submerged, growing in fresh water ponds. Roots conspicuous, dichotomous. Stems globose, 3-lobate, ca. 2 cm wide. Leaves 90-100 cm long, 0.2-0.3 cm wide at mid length, 50-60 per individual, linear, flexuous, erect, apex attenuate; alae 12-13 cm long, extending from the base ca. 1/10 of total leaf length, red-brown, membranaceous, apex attenuate; subula olive-green, trigonal. Labium present, persistent, 1.5-2.0 × 2.0-2.5 mm, cordate. Ligula not observed in herbarium material. Velum rudimentary. Sclerified phyllopodia absent. Sporangium at the base of the leaf, 8-12 × 3-4 mm, oblong, light brown, concolorous. Megaspores 310-390 µm in diameter (average = 350 µm, n = 20), trilete, white, not lustrous; proximal and distal surfaces pustulate, macrosculpture 3-8 × 22-45 µm, wider than high; laesurae 8-10 × 45-55 µm, at least four times wider than high. Microspores 31-36 µm long (average = 34 µm, n = 20), light brown, monolete, proximal surface smooth, distal surface sparsely echinate.

Distribution and habitat.

This species is only known from its type locality (state of Mato Grosso do Sul, Brazil; Fig. 3 ), where it grows in a fresh water pond at ca. 100 m a.s.l. Although we tried to re-collect Isoetes dubsii in the area indicated by Balthasar Dubs, no additional collections have been made.

Etymology.

The specific epithet honours the Swiss ornithologist and botanist B. Dubs, for his valuable contributions to the knowledge of the flora and fauna of the Pantanal wetlands of Brazil. He was also the first naturalist to collect Isoetes dubsii .

Notes.

Amongst the species found in Brazilian Pantanal wetlands, Isoetes panamensis Maxon C.V. Morton sensu lato is similar to I. dubsii due to its long leaves up to 80 cm. However, the megaspores in I. panamensis are 380-600 µm (vs. 310-390 µm) in diameter and baculate (vs. pustulate) ( Fig. 2 ).

Conservation status.

Since I. dubsii is currently known from a single locality, it may deserve special attention concerning its conservation status. However, based on our current knowledge on this species and according to IUCN Red List criteria ( IUCN 2012), it is assessed here as data deficient (DD).

Figures

Figure 1. Type of Isoetes dubsii (image courtesy of the herbarium Z / ZT). Note that the name Isoetes flexuosa J. B. S. Pereira on the label sheet is a provisional, never published, name. Photographer: Franziska Schmid

Figure 2. SEM images of the mega- and microspores of Isoetes dubsii (Dubs 829, Z / ZT), I. santacruzensis (Killeen et al. 7131, MO), I. pedersenii (Troels 8105, L) and I. panamensis (Balansa 3294, P).

Figure 3. Map showing the type locations of Isoetes dubsii and I. santacruzensis.