Isoetes santacruzensis J.B.S.Pereira

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

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Isoetes santacruzensis J.B.S.Pereira

sp. nov.

Isoetes santacruzensis J.B.S.Pereira  sp. nov. Figs 2View Figure 2, 4View Figure 4


Isoetes santacruzensis  is characterised by having flexuous, filiform leaves ranging from 0.4-0.8 mm wide at mid length and reaching up to 15 cm long, 15-30 leaves per individual, black or reddish-black sporangia, sclerified phyllopodia present, sparsely verrucate megaspores of 320-390 µm (average of 350 µm) in diameter.


BOLIVIA. Santa Cruz: Nuflo de Chaves, 15°32'40"S, 61°59'28"W, 450 m a.s.l., 11 Nov 1994, Killeen et al. 7131 (holotype: MO!).

Plant aquatic partially submerged or ephemeral terrestrial in rocky granite outcrops. Roots conspicuous, dichotomous. Stems globose, 3-lobate, 0.8-1.2 cm wide. Leaves 6-15 cm long, 0.4-0.8 mm wide at mid length, 15-30 per individual, filiform, flexuous, laxly ascending, apex attenuate; alae 0.3-3.5 cm long, extending from the base ca. 1/5 of total leaf length, hyaline or light brown, membranaceous, apex attenuate; subula olive green, trigonal. Labium present, persistent, cordate, 0.2-0.5 × 0.6-0.9 mm. Ligule not observed in herbarium material. Velum rudimentary to > 0.2 mm wide along the lateral edges of the sporangium. Sclerified phyllopodia present. Sporangium at the base of the leaf 2.5-3.5 × 2.0-2.5 mm, oblong, black or reddish-black, concolorous. Megaspores 320-390 µm in diameter (average = 350 µm, n = 20), trilete, white, not lustrous; proximal and distal surfaces sparsely verrucate, macrosculpture 10-25 × 19-31 µm, slightly wider than high; laesurae 26-30 × 16-21 µm, slightly higher than wide. Microspores 23-27 µm long (average = 25 µm, n = 20), light brown, monolete, proximal surface smooth, distal surface sparsely echinate.

Distribution and Habitat.

Isoetes santacruzensis  is only known from its type locality, where it grows as aquatic to ephemeral terrestrial in rocky granite outcrops, at elevations of about 450 m.


The specific epithet refers to the type region, the Department of Santa Cruz in Bolivia ( Fig. 3View Figure 3).


Until now, six species of Isoetes  were known from Bolivia, although the presence of unpublished species has already been mentioned ( Kessler and Smith 2018). Most of the known Bolivian species are from Andean habitats ( Kessler and Smith 2018) and have rugulate, laevigate ( Fig. 5View Figure 5) or tuberculate megaspores (see Hickey 1986b, Fig. 2View Figure 2) and laevigate, echinate or tuberculate microspores ( Fig. 5View Figure 5). Besides habitat, the macrosculpture of at least one of the spore types, megaspore or microspore, helps to differentiate I. santacruzensis  from the Andean Isoetes  species ( Figs 2View Figure 2, 4View Figure 4). Additionally, I. santacruzensis  is similar to I. pedersenii  by its small and verrucate megaspores. However, I. santacruzensis  can be readily distinguished by its erect and flexuous leaves (vs. ascending, linear and straight; Fig. 6View Figure 6), as well as by the characters present in the taxonomic key.

Conservation status.

Isoetes santacruzensis  is currently known from a single locality. The expansion of agricultural activities and cattle farming in this area show that this species may be prone to the effects of human activities within a very short time. However, given its potential occurrence in other areas and the lack of current knowledge about its distribution range, I. santacruzensis  should be assessed as data deficient (DD), according to IUCN criteria ( IUCN 2012).