Isoetes nana J.B.S. Pereira, 2017

Pereira, Jovani B. S., Stuetzel, Thomas & Schulz, Christian, 2017, Isoetes nana, a new species from the coastal mountains of southeastern Brazil, PhytoKeys 89, pp. 91-105 : 93-97

Isoetes nana J.B.S. Pereira sp. nov. Figs 1A-G ; 7A-C

Diagnosis.

Isoetes nana can be distinguished from its closely resembling species by a set of characters that include 5-15 small leaves per individual, erect, reaching up to 3.5cm long, megaspore rugulate (rarely laevigate or obscurely cristate) and microspore sparsely echinate.

Type.

BRAZIL. Rio de Janeiro: Serra de Itatiaia , March 1894, Ule 98 (holotype: G!; isotype: HBG!) .

Description.

Plants terrestrial or aquatic. Corm globose to subglobose, 0.3-0.8cm wide, 2-lobed. Roots conspicuous, dichotomously branched. Leaves 0.6-1.2mm wide at mid length, 1.5-3.5 cm long, 5-15, linear to triangular, straight, erect, apex acute; alae 0.9-1.6 cm long, stretching 1/2-3/4 of total leaf length. Subula semi-terete, olive-green in dry material. Labium present, caducous. Ligule not seen. Velum covering ca. 1/2 of the sporangium surface. Scales absent. Sporangium 1.0-1.5 mm wide, 1.5-2.0 mm long, orbiculate to elliptic, hyaline throughout. Megaspore 480-520 µm diameter (average = 500 µm, N = 10), trilete, white, not lustrous, subspheroidal; laesures straight, narrowly triangular, higher than wide, with straight and parallel sides, apex acute, slightly lower close to the pole; macrosculpture of the proximal and distal surfaces rugulate (rarely laevigate or obscurely cristate), microsculpture of the proximal and distal surfaces with terminal ends of anastomosed bars joined forming bacillae or more rarely echinulae; equatorial ridges arched, with straight and parallel sides, rounded. Microspore 29-33µm long (average = 31 µm, N = 20), light brown, monolete; laesurae straight, without prominent invagination, macrosculpture on the proximal and distal surface sparsely echinate, echinulae low, microsculpture baculate and granulate.

Additional specimens examined.

BRAZIL. Rio de Janeiro: Serra de Itatiaia , em pequenas bacias d’água dos rochedos, Mar. 1894, Ule s.n. (P01591972; https://science.mnhn.fr/institution/mnhn/collection/p/item/p01591972) .

Distribution and habitat.

Isoetes nana is known only from the type locality at Serra de Itatiaia, Rio de Janeiro (Figure 2 ). According to the label on herbarium sheets, the population was found at elevations of about 2300 m and recorded as aquatic, growing in small ponds on rocky outcrops.

Comments.

The two collections (Ule 98, kept in G and HBG and Ule s.n. kept in P) made by Ule at Serra de Itatiaia (Rio de Janeiro, Brazil) in March 1894 are probably a single collection. Fuchs-Eckert labelled the collection Ule 98 (G) as Isoetes nana and also cited this name in a published paper ( Fuchs-Eckert 1982: 255). Hickey (1985) also pointed out the unique characters of the megaspore of I. nana in his doctoral thesis ( Hickey 1985: 142). However, neither Fuchs-Eckert nor Hickey have diagnosed and validly published this new taxon. Isoetes nana is known only from these two collections. Although we tried three times to re-collect Isoetes nana , without success (all our attempts were with bad weather, including heavy rain), no additional collections have been made until now. The lack of recent collections of this species may probably be due to two main reasons: first, because of its rarity; second, because it has been overlooked (as many Isoetes species) by botanists during fieldwork.

In the same Serra do Itatiaia, three other Isoetes taxa occur: I. ulei U. Weber, I. martii A. Braun and I. x goebelii U. Weber (pro sp.) ( I. martii × Isoetes sp.) (Figs 3 - 5 ). Isoetes nana can be easily distinguished from these species and the hybrid by its few leaves (5-15 per individual vs. more than 15 per individual, rarely 10 leaves in I. martii ) that are short (1.5-3.5 cm vs.> 6 cm) and by its megaspore rugulate, rarely laevigate or obscurely cristate (vs. reticulate or distinctly cristate) and microspore sparsely echinate (vs. laevigate or densely echinate) (Table 1 - 2 ).

In the coastal mountains in southern Brazil, three other species with non-reticulate megaspore occur that are similar to this new species (Figure 2 ; Table 1 - 2 ): I. weberi U. Weber (Figures 6A-C , 7D-F and 8A-C ), I. quiririensis J.B.S. Pereira & Labiak (Figures 6D-F , 7G-I and 8D-F ) and I. maxima Hickey, Macluf & Link-Pérez (Figures 6G-I , 7J-L and 8G-I ). Isoetes nana can be distinguished by the characters shown in the following taxonomic key and in Tables 1 and 2 . Furthermore, although the microsculpture of the megaspore seems to be a reliable source of taxonomic characters and it has been widely used to separate species in Selaginella ( Schulz et al. 2013; Bauer et al. 2016), the megaspore microsculpture in Isoetes is rarely studied and used in the taxonomy (but see Macluf et al. 2003; Troia et al. 2012; Schafran et al. 2016). We observed that the microsculpture of the proximal-distal surfaces of the megaspores of I. nana consists of anastomosed bars, whose terminal ends are joined forming bacillae or more rarely echinulae (Figure 7C ). Amongst the analysed species, only I. maxima shows a similar microsculpture pattern (Figure 7L ), while all remaining species present terminal ends of anastomosed bars joined forming echinulae (or more rarely bacillae in I. quiririensis ) (Figures 4C, F, I and 7F, I ). These data show that megaspore microsculpture may provide useful characters not only to identify I. nana , but also for the taxonomy of Brazilian Isoetes .

Since there is a correlation between spore sizes and ploidy level (Kott and Britton 1980; Troia 2001; Pereira et al. 2015) and I. nana presents mega- and microspore sizes that are similar to those of the diploids I. quiririensis and I. maxima (Table 2 ), we hypothesise that I. nana is also diploid.

Conservation status.

Since I. nana is currently known from a single (not recently confirmed) 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. Isoetes nana sp. nov. (from the holotype: Ule 98, G). A 1 - 4 Habit (images are courtesy of the herbarium G) B-D Megaspore B Proximal view of an obscurely cristate (B 1) and rugulate (B 2) megaspore C Distal view (<* portion of the megaspore covered by sporangium tissue) D Equatorial view E-G Microspore E Proximal view F Equatorial view G Distal view. Scale bars: A 1 - 4 = 1 cm; B-D = 100 µm; E-G = 2 µm.

Figure 2. Geographical distribution of Isoetes nana (blue circle), I. maxima (purple triangle), I. quiririensis (orange diamond) and I. weberi (green squares) in southeastern South America. In Brazil: MG = Minas Gerais; PR = Parana; RJ = Rio de Janeiro; RS = Rio Grande do Sul; SC = Santa Catarina; SP = Sao Paulo.

Figure 3. SEM images of the megaspore of Isoetes ulei (Ule 3533, HBG), I. martii (Pereira 720, UPCB) and I. x goebelii (Pereira 718, UPCB). A-C Megaspore of I. ulei A Proximal view B Distal view C Equatorial view D-F Megaspore of I. martii D Proximal view E Distal view F Equatorial view G-I Megaspore of I. x goebelii G Proximal view H Distal view I Equatorial view. All scale bars = 100 µm.

Figure 4. SEM images of the megaspore of Isoetes ulei (Ule 3533, HBG), I. martii (Pereira 726, UPCB) and I. xg oebelii (Pereira 718, UPCB). A-B Details of the macrosculpture of the megaspore of I. ulei A Proximal view B Distal view C Details of the microsculpture of the megaspore of I. ulei in distal view showing the terminal ends of anastomosed bars joined forming echinulae D-E Details of the macrosculpture of the megaspore of martii D Proximal view. E. Distal view F Details of the microsculpture of the megaspore of martii in distal view showing the terminal ends of anastomosed bars joined forming echinulae G-H Details of the macrosculpture of the megaspore of I. x goebelii G Proximal view H Distal view I Details of the microsculpture of the megaspore of I. x goebelii in distal view showing the terminal ends of anastomosed bars joined forming echinulae. Scale bars: A, B, D, E, G, H = 10 µm; C, F, I = 1 µm.

Figure 5. SEM images of the microspore of Isoetes ulei (Ule 3533, HBG), I. martii (Regnel 1505, B) and I. x goebelii (Pereira 718, UPCB). A-C Microspore of I. ulei A Proximal view B Distal view C Equatorial view D-F Microspore of I. martii D Proximal view E Equatorial view F Distal view G-I Microspore of I. x goebelii G Proximal view H Equatorial view I Equatorial view. All scale bars = 2 µm

Figure 6. SEM images of the megaspore of Isoetes weberi (Herter 95840, US), I. quiririensis (Pereira 635, UPCB), I. maxima (Pereira 631, UPCB). A-C Megaspore of I. weberi A Proximal view B Distal view C Equatorial view D-F Megaspore of I. quiririensis D Proximal view E Distal view F Equatorial view G-I Megaspore of I. maxima J Proximal view K Distal view L Equatorial view. All scale bars = 100 µm.

Figure 7. SEM images of the megaspore of Isoetes nana (Ule 98, G), I. weberi (Herter 95840, US), I. quiririensis (Pereira 635, UPCB), I. maxima (Pereira 631, UPCB). A-B Details of the macrosculpture of the megaspore of I. nana A Proximal view B Distal view C Details of the microsculpture of the megaspore of I. nana in distal view showing the terminal ends of anastomosed bars joined forming bacillae or more rarely echinulae D-E Details of the macrosculpture of the megaspore of I. weberi D Proximal view E Distal view F Details of the microsculpture of the megaspore of I. weberi in distal view showing the terminal ends of anastomosed bars joined forming echinulae G-H Details of the macrosculpture of the megaspore of I. quiririensis G Proximal view H Distal view I Details of the microsculpture of the megaspore of I. quiririensis in distal view showing the terminal ends of anastomosed bars joined forming echinulae or rarely bacillae J-K Details of the macrosculpture of the megaspore of I. maxima J Proximal view K Distal view L Details of the microsculpture of the megaspore of I. maxima in distal view showing the terminal ends of anastomosed bars joined forming bacillae. Scale bars: A, B, D, E, G, H, J, K = 10 µm; C, F, I, L = 1 µm.

Figure 8. SEM images of the microspore of Isoetes weberi (Herter 95840, US), I. quiririensis (Pereira 635, UPCB), I. maxima (Pereira 631, UPCB). A-C Microspore of I. weberi A Proximal view B Equatorial view C Distal view D-F Microspore of I. quiririensis D Proximal view E Equatorial view F Distal view G-I Microspore of I. maxima G Proximal view H Equatorial view I Distal view. All scale bars = 2 µm.