Abstract
Isoetes dubsiisp. nov. and I. santacruzensissp. nov., two new species from lowland areas in South America, are described, illustrated and compared to similar species. Isoetes dubsii can be distinguished from other species of the Brazilian Pantanal wetlands by a set of characters including leaves that are long, flexuous and trigonal in transverse section, tri-lobate stems, rudimentary velum, pustulate megaspores of 310‒390 µm diameter and laesurae of the megaspore at least four times wider than high. Isoetes santacruzensis has flexuous, filiform leaves, 0.4–0.8 mm wide at mid length and reaching up to 15 cm long, black or reddish-black sporangia, sclerified phyllopodia and sparsely verrucate megaspores of 320‒390 µm in diameter. We also include a key for species from the Brazilian Pantanal wetlands and Bolivia and spore images for all species that are discussed. Isoetes dubsii and I. santacruzensis are only known from their type localities and they may deserve special attention concerning their conservation status. However, based on our current knowledge on these species and according to IUCN Red List criteria, they are assessed here as data deficient (DD).
Highlights
Herbarium collections are amongst the most important tools for obtaining information about the composition, distribution and content of plant diversity in a given region (Nualart et al 2017)
Our recent efforts to access the diversity of Isoetes in South America has led us to consult herbarium collections where we discovered two species that we recognised as undescribed
One of the new species is from Bolivia and the other is from Pantanal wetlands in Brazil
Summary
Herbarium collections are amongst the most important tools for obtaining information about the composition, distribution and content of plant diversity in a given region (Nualart et al 2017). Keywords Aquatic plants, Bolivia, Brazil, herbarium collections, lycophytes, Isoetes, Pantanal wetlands, spores. The use of SEM adds logistic difficulties in the taxonomy of the genus and, as a result, many Isoetes species remain unidentified and/or undescribed in herbarium collections.
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