Isoetes gardneriana Kunze ex A. Braun, Verh. Bot. Vereins Prov. Brandenburg 4: 330. 1862.

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 gardneriana Kunze ex A. Braun, Verh. Bot. Vereins Prov. Brandenburg 4: 330. 1862.

Description.

Stems globose, 2.5-4 cm wide, 3 or 4-lobate. Leaves 1.0-1.8 mm wide at mid length, 32-45 cm long, 30-90 per individual, linear, straight, ascending, apex acute; alae 7-15 cm long, extending from the base 1/5-2/5 of total leaf length, hyaline or light brown, chartaceous, attenuate. Subula present, olive green, trigonal. Labium present, 2.5-3.5 × 4-6 mm, cordate. Ligule not observed. Velum> 0.4 mm along the lateral edges of the sporangium, rudimentary. Sclerified phyllopodia absent. Sporangium at the base of the leaf, 8-18 × 4.3-7 mm, oblong, hyaline, brown dots absent. Megaspores grey, 490-650 µm in equatorial diameter (average = 540 µm), trilete; laesures higher than wide, 40-50 × 11-16 µm; proximal surface tuberculate, macrosculptural projections 20-39 × 13-24 µm; equatorial ridges arched, straight; distal surface tuberculate, projections 24-44 × 17-34 µm. Microspores 33-40 µm long (average = 37 µm), proximal and distal surface smooth or sparsely microechinate.

Type.

Brazil. Province of Goyaz: Missiones Duro, Sept 1841, Gardner 3563, (holotype: B! [B200107577]; isotype: BM [BM000097912,] E! [E00429095], K! [K000574505]).

Remarks.

Despite our intensive fieldwork efforts in the Brazilian Cerrado, I. gardneriana was only rediscovered in Terenos in the state of Mato Grosso do Sul at the geographical coordinates 20°33'32"S, 54°47'23"W. This area is located at about 1200 km away from its type location ( Fig. 1A ). It was collected there by both Vali Pott in September 2010 (Pott 11018, CGMS) and Jovani Pereira in November 2017 (Pereira 1028, MG) after 167 and 175 years, respectively. Although these records were far from the type location, habitat and morphology of this newly collected population are almost identical to the type.

Isoetes gardneriana was found in a pond along with Rhynchospora corymbosa (L.) Britton, Pontederia cordata L. and Xyris spp. ( Fig. 1D ). This pond occurred by the side of a “vereda”, which showed a clay and hydromorphic soil and an open vegetation physiognomy with the presence of numerous “buriti” palms ( Mauritia flexuosa L.f.) that grow over a dense herbaceous stratum. The life form of I. gardneriana was of a partially submerged aquatic in September, although in November, plants were found both partially and totally submerged ( Fig. 1E ). The total monthly precipitations were 127 and 315.8 mm in September 2010 and November 2017, respectively ( CEMTEC/MS 2019). The average monthly maximum and minimum temperatures were 32 and 22 °C, respectively ( CEMTEC/MS 2019). The maximum and minimum temperature averages were 32.7 and 19.6 °C, respectively, in September 2010. In November 2017, the average monthly maximum and minimum temperatures were 30.7 and 20 °C, respectively ( CEMTEC/MS 2019).

Morphologically, the individuals have ascending leaves, rudimentary vela, elliptic sporangia and 3-lobate corms (or more rarely 4). The megaspores are brown, sparsely verrucate, 490-650 µm diameter (vs. 548-615 µm), with knife-like laesurae ( Fig. 2 ). The microspores are echinate, 33-40 µm long (vs. 34-38 µm) ( Fig. 2 ).

On the other hand, none of the analysed herbarium collections appeared (Balansa 3294, Irwin 31615 and Labiak 5783) to be I. gardneriana . The megaspores of these collections are both qualitatively and quantitatively distinct from the type of I. gardneriana . The Balansa and Labiak collections have baculate-tuberculate megaspores and Irwin’s collection revealed baculate-clavate megaspores ( Fig. 3 ), which confirm that these materials represent variants of I. panamensis s.l. Additionally, the macro-ornamentation projections of the megaspores of I. gardneriana are, in general, narrower and shorter than those found in I. panamensis s.l. ( Fig. 4 ).

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.

Figure 3. Megaspores of the variants of Isoetes panamensis sensu lato.

Figure 4. Boxplots showing quantitatively the variation in the size of the macro-ornamentation projections of the megaspores of I. gardneriana and I. panamensis sensu lato. In the proximal surface, the projects of the macro-ornamentation are narrower and shorter in I. gardneriana than in I. panamensis s. l. In the distal surface, the macro-ornamentation projections are slightly narrower and considerably shorter in I. gardneriana than in I. panamensis s. l ..