Isoetes amazonica A. Braun, J. Bot. 18: 109. 1880.

Pereira, Jovani B. S., Giulietti, Ana Maria, Pott, Vali J. & Watanabe, Mauricio T. C., 2019, Rediscovering two Isoetes species in the Brazilian Amazon and Cerrado after 167 years, PhytoKeys 135, pp. 105-117 : 105

Isoetes amazonica A. Braun, J. Bot. 18: 109. 1880.

Description.

Stems globose, 0.35-0.7 cm wide, 3-lobate. Leaves 0.45-1 mm wide at mid length, 4-17 cm long, 9-23 per individual, filiform, straight, ascending, apex acute; alae 0.8-4.5 cm long, extending from the base 1/10 - 1/4 of total leaf length, hyaline, membranaceous, attenuate. Subula present, olive green, trigonal. Labium present, 0.5-0.7 × 0.9-1.1 mm long, cordate. Ligule 2.5-3 × 1-1.2 mm, hyaline, triangular. Velum 0.1-0.2 mm along the lateral edges of the sporangium, rudimentary. Sclerified phyllopodia absent. Sporangium at the base of the leaf, 2-2.5 × 1.8-2.5mm, elliptic, hyaline, light brown, brown dots present or absent. Megaspores white, 420-512 (-590) µm in equatorial diameter (average = 490 µm), trilete; laesurae as wide as high or higher than wide, 40-53 × 35-47 µm; proximal surface verrucate, projections 24-41.4 × 24-46 µm; equatorial ridges arched, slightly sinuous; distal surface verrucate, macroscuptural projections 25-45 × 25-46 µm. Microspores 28-32 µm long (average = 30 µm), proximal surface echinate, distal surface sparsely echinate.

Type.

Brazil. Province of Pará: inundated places near Santarém, Sept 1850, Spruce 1081, (holotype: B! [B200107121]; isotype: K! [K000574506], P! [P00573942; P00573943]).

Remarks.

Isoetes amazonica was rediscovered at its type location in July 2017 after 167 years (Pereira 1015, MG). This species was found in a single area at approximately 2.5 km from the left bank of the Tapajós river at the geographical coordinates 2°24'15.15"S, 55°3'1.89"W ( Figure 1A ). This location was a marsh area between a flooded forest and cattle farming. The plants were found as terrestrials in wet clay and sandy soils ( Fig. 1B, C ). None of the individuals was completely submerged (but see discussion). The monthly precipitation was 42.4 mm and it was the lowest recorded value for July between the years of 2008 and 2017 ( INMET 2019). The average monthly maximum and minimum temperatures were 32 and 22 °C, respectively ( INMET 2019). This species occurred in association with other plant groups such as Cyperaceae , Poaceae , Mayacaceae and Eriocaulaceae . The newly rediscovered population showed typical characteristics of I. amazonica , such as 10-20 leaves per individual, ascending leaves, rudimentary velum, hyaline sporangia with or without brown spots, verrucate megaspores with 470-590 µm diameter, sparsely echinate microspores 28-32 µm long ( Fig. 2 ).

Figures

Figure 1. Geographic distribution, habit and habitat of Isoetes amazonica and I. gardneriana A location where Isoetes amazonica and I. gardneriana were rediscovered in Brazil (type location of I. gardneriana in blue pentagon) B-C Isoetes amazonica (Pereira 1015, MG): B habitat C habit D-E Isoetes gardneriana (Pereira 1028, MG): D habitat E habit.

Figure 2. Mega- and microspores of Isoetes amazonica and I. gardneriana.