Three new species of Isoetes (Isoetaceae) are described from the Democratic Republic of the Congo, Rwanda and Burundi for inclusion in the family treatment for the Flore d'Afrique Centrale. Isoetes hallei sp. nov. is related to I. alstonii and I. schweinfurthii, I. rwandensis sp. nov. to I. abyssinica and I. welwitschii, and I. pichisermollii sp. nov. to I. abyssinica and I. schweinfurthii. The differences between these species are discussed and geographical distribution maps for the new species are presented. The conservation status of the new species is preliminarily assessed. The megaspores of the type specimens of I. abyssinica, I. alstonii, I. schweinfurthii and I. welwitschii were studied using Scanning Electron Microscopy to distinguish the new species from the more similar other ones.
Citation: Fischer E. & Lobin W. 2022: The genus Isoetes (Isoetaceae) in Central Africa (Democratic Republic of the Congo, Rwanda, Burundi) with the description of three new species. – Willdenowia 52: 315–334.
Version of record first published online on 1 December 2022 ahead of inclusion in December 2022 issue.
Introduction
Isoetes Linnaeus (1753: 1100) is an almost cosmopolitan genus of heterosporous lycophytes, containing more than 200 species (Troia & al. 2016), and is the only living representative of the family Isoetaceae (Jermy 1990).
The last worldwide taxonomic monograph of Isoetes was published by Pfeiffer (1922). This monograph included 77 taxa (65 species, eight varieties, and four forms). Pfeiffer (1922) counted only four taxa in Africa. Troia & al. (2016) listed 12 species for tropical Africa. Isoetes species are rarely collected (see below), because they resemble sterile Eleocharis spp. or similar Cyperaceae or Poaceae.
Identification of Isoetes species is largely based on megaspore and microspore micromorphology (Hickey 1986; Pereira & al. 2016). There are only a few other reliable characters, such as number and size of leaves, presence of a velum, and leaf anatomy (Verdcourt 2005). As a result of an increasing number of studies using micromorphology, several new Isoetes species have recently been described, among them even taxa from Europe (e.g. I. todaroana Troia & Raimondo 2009: 238; I. sabatina Troia & Azella 2013: 1; I. haussknechtii Troia & Greuter 2015: 395) and Turkey (I. vanensis Keskin & Zare in Zare & al. 2016: 295).
During the preparation for the treatment of Isoetaceae for the Flore d'Afrique Centrale (Democratic Republic of the Congo [hereafter “D. R. Congo”], Rwanda, Burundi) we found only few collections in the different herbaria. For the whole D. R. Congo, there is a single collection from the surroundings of Kinshasa deposited at Meise (BR), which proved to be a new species.
Likewise for the whole D. R. Congo there is only one record for Isoetes welwitschii from Kahuzi-Biéga National Park (Mt Biega), published by Mangambu Mokoso & al. (2013). Because we have seen only a photograph of the specimen, we could not verify this identification. In the distribution list for I. welwitschii, Mangambu Mokoso & al. (2013) also cited Rwanda, which is erroneous. Records of I. abyssinica were also published for Burundi (Pichi Sermolli 1983, 1985) and for Rwanda (Fischer & Hinkel 1992; Fischer & Frankenhäuser 1994). Both these records were misidentified and represent species new to science. Therefore, for Central Africa (D. R. Congo, Rwanda, Burundi) three new species and an as yet unidentified taxon have been recorded. These three new species are described below (see Taxonomic treatment).
We anticipate the number of species to be much higher because the region provides numerous potential habitats, such as small, temporary rock pools and dambos (i.e. seasonally flooded rock outcrops or lateritic crusts) in NE D. R. Congo (e.g. Parc National de Garamba), in Haut Katanga or near the border with Angola. In neighbouring countries, including Angola, Zambia, Tanzania and South Sudan, four additional Isoetes species have been identified (I. aequinoctialis, I. alstonii, I. schweinfurthii and I. welwitschii), and these are likely to occur in Central Africa as well.
Another purpose of this paper, as a precursor to a revision of the Tropical African species of Isoetes, was to study species delimitations. The most reliable characteristic is the megaspore micromorphology, but this is difficult to apply in the field (e.g. Verdcourt 2005). Therefore, we studied the type material of different species, e.g. I. abyssinica, I. alstonii, I. schweinfurthii and I. welwitschii and made SEM micrographs from the megaspores for comparison. We choose these species because they are morphologically similar and have been confused with the new taxa from Central Africa. Some of the SEM micrographs are published for the first time.
Material and methods
The present study is based on the investigation of living plants and dried herbarium specimens from the following herbaria: B, BR, FT and K (abbreviations after Thiers 2022+). The information about the habitat of the species in question is based on field observations and herbarium labels. Additional field work was performed in D. R. Congo, Rwanda and Burundi including more than 118 fieldtrips since 1984.
Most of the specimens studied can also be consulted online: B ( http://ww2.bgbm.org/herbarium/), BR ( https://www.botanicalcollections.be/) and K ( http://apps.kew.org/herbcat/). The megaspores were sputtered with gold by a Balzers Union SCD 040 and photographed with a Leo 1450 scanning electron microscope at the Nees Institute for Biodiversity of Plants, University of Bonn. The terminology for megaspore ornamentation follows Hickey (1986). The phytogeographical divisions follow Flore d'Afrique Centrale (Bamps 1982).
Results
Megaspore micromorphology of selected African Isoetes taxa
We have described and illustrated the megaspores of types of selected African Isoetes together with other material from the distribution area in order to define the species. The general terminology was introduced by Hickey (1986). Various authors (e.g. Hickey 1986; Pereira & al. 2016) described a secondary ornamentation. This is considered here as hydrophobic and wax-like (Barthlott & al. 1998; Barthlott & al. 2016, 2017), representing waxes with a characteristic structure. In the case of the studied species of Isoetes they are called threads (Barthlott & al. 1998: 244), i.e. massive crystalloids with a circular cross-section and a length/width ratio of more than 100:1. These very fine, long crystalloids often form a felt-like covering (see also Wollenweber 1984; Barthlott & Wollenweber 1981). Sometimes the short threads also resemble rodlets. The orientation follows the ornamentation of the spore surface (Barthlott & Wollenweber 1981).
To assess the megaspore variation, we investigated three different gatherings of Isoetes schweinfurthii, the type specimen from South Sudan, and material from Benin and Tanzania (Fig. 4–6). The variation is very limited and a clear set of character states for the species can be described. This supports the view that megaspores are a very reliable character for distinguishing Isoetes species. This is also true for other groups of ferns and lycophytes (e.g. Chen & al. 2022).
Isoetes abyssinica Chiov. in Atti Soc. Naturalisti Mat. Modena 64: 45. 1933. – Lectotype (designated here, following Jermy in sched.): Ethiopia, Amhara – Dembià, valle Cococc sopra Gondar, pascoli rocciosi aprici lungo rigagnoli asciutti, 3 Sep 1909, Chiovenda 1809 (FT006224). – Fig. 1.
Description — Megaspores c. 480 × 460–480 µm; proximal face trilete, densely pustulate, pustules 20–50 µm in diam., not anastomosing, sometime tuberculate, tubercles thin in between, 7.5–15 µm in diam., waxes with threads slightly felty, ridges c. 50 µm wide and c. 20 µm high; distal face clavate with distant projections up to 60 µm high and 40–50 µm in diam. and small tubercles 20–24 µm in diam. in between, densely covered by short threads, clavate projections above with short or lacking threads. – Fig. 2.
Isoetes alstonii C. F. Reed & Verdc. in Kirkia 5: 19. 1965. – Holotype: Zimbabwe, Victoria Falls, S bank in front of main falls, under the spray of the main falls, 29 Aug 1947, Greenway & Brenan 8012 (EA [not seen]; isotype: K000351301).
Description — Megaspores 400–520 × 480–520 µm; proximal face trilete, densely tuberculate-pustulate, with large projections 30–60 µm in diam. and up to 20 µm high, and smaller projections 19–22 µm in diam., with dense threads covering tubercles and most of pustules, ridges up to 30 µm wide and up to 40 µm high; distal face with few large and distant pustules 40–60 µm in diam. and up to 20 µm high, and small tubercles 20–30 µm in diam., tubercles with short and dense threads, pustules free of waxes. – Fig. 3.
Isoetes schweinfurthii A. Braun ex Baker in J. Bot. 18: 108. 1880. – Lectotype (designated by Schelpe & Anthony 1986: 28): South Sudan, 2–4′ [Fuß] unter Wasser in einem Regenlauf bei der großen Seriba Ghattas im Djurgebiet, 20 Jun 1869, Schweinfurth 1962 ( B 20 0108240; isolectotypes: B 20 0108246, B 20 0108247, K000351298).
Fig. 1.
Lectotype of Isoetes abyssinica, Chiovenda 1809 (FT006224). – © Herbario Tropicale Firenze, reproduced with permission.
Fig. 2.
SEM micrographs of megaspores from Isoetes abyssinica (lectotype, Chiovenda 1809, FT006224). – A: distal view; B, C: details from distal view showing thread cover; D: proximal view; E, F: details from proximal view showing thread cover. – Scale bars: A, D = 200 µm; C, F = 80 µm; B, E = 30 µm.
Fig. 3.
SEM micrographs of megaspores from Isoetes alstonii (isotype, Greenway & Brenan 8012, K000351301). – A: distal view; B, C: details from distal view showing thread cover; D: proximal view; E, F: details from proximal view showing thread cover. – Scale bars: A, D = 200 µm; B, E = 80 µm; C, F = 30 µm.
Fig. 4.
SEM micrographs of megaspores from Isoetes schweinfurthii (lectotype Schweinfurth 1962, B 20 0108240). – A, B: distal view; C, D: details from distal view showing thread cover; E: proximal view; F: details from proximal view showing thread cover. – Scale bars: A, B, E = 200 µm; C, F = 80 µm; D = 30 µm.
Fig. 5.
SEM micrographs of megaspores from Isoetes schweinfurthii (Van der Maesen & al. 7203, BR0000015469366). – A: distal view; B, C: details from distal view showing thread cover; D: proximal view; E, F: details from proximal view showing thread cover. – Scale bars: A, D = 200 µm; B, E = 80 µm; C, F = 30 µm.
Fig. 6.
SEM micrographs of megaspores from Isoetes schweinfurthii (Bidgood & al. 7304, K001291892). – A: distal view; B, C: details from distal view showing thread cover; D: proximal view; E, F: details from proximal view showing thread cover. – Scale bars: A, D = 200 µm; B, E = 80 µm; C, F = 30 µm.
Fig. 7.
SEM micrographs of megaspores from Isoetes welwitschii (isotype, Welwitsch 166, K000351303). – A: equatorial view; B: details from equatorial showing thread cover; C: proximal view; D: details from proximal view showing thread cover; E, F: details from equatorial view with distal face, showing thread cover. – Scale bars: A, C = 200 µm; B, D, E = 80 µm; F = 40 µm.
Fig. 8.
A: holotype of Isoetes hallei, Hallé 1922 (BR0000015460486); B: details from holotype. – © Meise Botanical Garden, reproduced with permission. – Scale bar: B = 1 cm.
Fig. 9.
SEM micrographs of megaspores and sporangium from Isoetes hallei (holotype, Hallé 1922, BR0000015460486). – A, B: equatorial view; C: distal view; D: details from distal view showing thread cover; D: proximal view; E: base of leaf with mega-sporangium (adaxial); F: details from proximal view showing thread cover. – Scale bars: A–C, F = 30 µm; D = 200 µm; E = 1 mm.
Fig. 10.
Holotype of Isoetes pichisermollii, Reekmans 4400 (K001291890). – © Royal Botanical Gardens, Kew, reproduced with permission.
Fig. 11.
SEM micrographs of megaspores from Isoetes pichisermollii (holotype, Reekmans 4400, K001291890). – A: distal view; B, C: details from distal view showing thread cover; D: equatorial view; E, F: details from proximal view showing thread cover. – Scale bars: A, D = 200 µm; C, E = 80 µm; B, F = 30 µm.
Fig. 12.
Isoetes rwandensis – A: habitat; B, C: plants. – All photographs taken at the type locality, 9 Jan 2012, by and © Eberhard Fischer. – Scale bars: B, C = 1 cm.
Fig. 13.
SEM micrographs of megaspores from Isoetes rwandensis (holotype, Fischer 66/2012, BR0000015253576V). – A, B: proximal view; C: distal view; D: equatorial view; E: details from distal view showing thread cover; F: base of leaf with mega-sporangium. – Scale bars: F = 1 mm; A–D = 100 µm; E = 30 µm.
Description — Megaspores (360–)440–520 × (360–) 440–520 µm; proximal face trilete, laevigate or with up to 3 flat tubercles c. 22.5 µm high and up to 15 µm in diam. per areole, covered with dense threads, ridges c. 60 µm wide and 20–30 µm high, free of waxes; distal face with dense to distant pustules 20–40 µm in diam., partly smaller, anastomosing, larger pustules 80–100 µm in diam., all covered with dense threads. – Fig. 4–6.
Additional specimens studied — Benin: Atakora: Matéti, SE of Dassari, along RNIE (Route Nationale) 3, 10°48.3′N, 01°09.3′E, dried up rice fields, 22 Nov 1999, Van der Maesen, Akoegniaou, Yédomonhau & Agbani 7203 (BR0000015469366). — Tanzania (T4): TABORA: 21 km on Tabora–Urambo road, 05°05′S, 32°39′E, 1025 m, 11 Jun 2008, Bidgood, Leloyo & Vollesen 7304 (K001291892).
Isoetes welwitschii A. Braun in Kuhn, Filic. Afr.: 196. 1868. – Holotype: Angola, “Habit.[at] socialis cum Xyridis, Ophioglosso et Cyperaceis in pascuis editis subspongiosis in planitie de Empalanca territoriiis Huillensis”, Apr 1860, Welwitsch 166 ( B 20 0108478; isotype: K000351303).
Description — Megaspores c. 400 × 400–440 µm; proximal face trilete, with scattered and large and distant pustules 20–30 µm high and 30–40 µm in diam., and small tubercles 10–20 µm in diam. in between and toward ridges, with sparse threads, ridges free of waxes; distal face with large pustules up to 40 µm high and 30–40 µm in diam., partly anastomosing, and with small tubercles 16–20 µm in diam. toward margin, with sparse threads. – Fig. 7.
Note — Welwitsch wrote on the Kew specimen in ink: “Obs Omnia specimina a me visa habitu et statura pusilla inter se perfecte aequalia!”
Taxonomic treatment
Isoetes hallei Eb. Fisch. & Lobin, sp. nov. – Fig. 8–9, 14A.
Holotype: D. R. Congo, Bas-Congo, Zongo, Kasangulu, chutes, 8 Apr 1971, Hallé 1922 (BR0000015460486).
Diagnosis — The new species resembles Isoetes alstonii and I. schweinfurthii but differs from both in the stouter habit and much shorter leaves (20–25 mm vs 150–400[–600] mm). The megaspores are slightly larger (c. 560 × 480 µm vs 400–520 × 480–520 µm in I. alstonii and 360–520 × 360–520 µm in I. schweinfurthii). The proximal face is densely pustulate with larger and smaller pustules, sometimes anastomosing, whereas in I. alstonii the proximal face is densely tuberculate-pustulate, with larger and smaller projections, never anastomosing, and in I. schweinfurthii the proximal face is laevigate or bears 3 tubercles at most.
Description — Corm 3-lobed, 5–13 mm wide, bud scales absent. Leaves 12–38, 20–25 mm long, c. 3 mm wide at base, 0.9–1 mm wide at apex, tapering gradually to a slender point. Ligule not seen. Velum rudimentary to absent. Megasporangia c. 5 × 2.5 mm, ovate, sporangial wall pale. Megaspores c. 560 × 480 µm; proximal face trilete, densely pustulate, with densely large and small pustules, sometimes anastomosing, 48–60 µm in diam., wax-like structures sometimes rodlet-like and filiform threads on pustules and dense threads between pustules, larger pustules partly anastomosing, ridges also partly pustulate, up to 60 µm wide and 60 µm high; distal face densely pustulate with large and smaller intermixed pustules, large pustules 45–57 µm in diam., partly anastomosing, small pustules 30–38 µm in diam., pustules almost completely covered with dense threads, sometimes rodlet-like. Microspores not seen.
Distribution — Known only from the type locality in western D. R. Congo (Fig. 14A).
Habitat — On wet rocks in waterfalls, probably perennial, c. 320 m.
IUCN conservation assessment (preliminary) — Critically Endangered: CR B2ab(iii). Isoetes hallei is known only from the type locality. The last two collections were made c. 50 years ago. The estimated AOO is 4 km2 (assuming a 4 km2 grid cell size). The habitat, a waterfall, is actually not protected, but there seem to be no immediate threats.
Etymology — Named after Francis Hallé (born 1938), who first collected the new species.
Additional specimens studied — D. R. Congo: Bas-Congo: chutes de Zongo, dans une pente rocheuse mouillée d'embruns, 21 Feb 1971, F. Hallé 1900 ( P01590086).
Isoetes pichisermollii Eb. Fisch. & Lobin, sp. nov. – Fig. 10–11, 14B.
Holotype: Burundi, Bubanza district, Rusizi plain, km 14, 800 m, temporary swamp, 16 Mar 1975, Reekmans 4400 (K001291890).
Diagnosis — The new species differs from Isoetes abyssinica in the much longer leaves (240–460 mm vs 114–188 mm) and in the megaspore micromorphology. The megaspores are smaller (c. 400 × 400 µm vs c. 480 × 460–480 µm in I. abyssinica). The distal face in the new species has spaced larger and smaller pustules, whereas in I. abyssinica the distal face is clavate with distant projections and small tubercles in between. The new species also differs from I. schweinfurthii, which has a similar leaf length, in the megaspore micromorphology. The megaspores are smaller (c. 400 × 400 µm vs (360–) 440–520 × (360–)440–525 µm in I. schweinfurthii). The proximal face bears spaced tubercles 7–11 per trilete surface, whereas in I. schweinfurthii it is laevigate or bears 3 tubercles at most.
Fig. 14.
A: distribution map of Isoetes hallei (black circle). – B: distribution map of I. rwandensis (yellow circles) and I. pichisermollii (red circles). – Red lines indicate country borders, blue lines and surfaces rivers and lakes. – Scale bars: A = 1500 km; B = 100 km.
Description — Corm 3-lobed, 10–20 mm wide, bud scales c. 9 × 4 mm, cuspidate, blackish. Leaves (6–)10 or 11, 240–400(–460) mm long, 4–5 mm wide at base, c. 1 mm wide at apex, tapering gradually to a slender apex. Ligule not seen. Velum absent. Megasporangia c. 5 × 3 mm, sporangial wall pale. Megaspores c. 400 × 400 µm; proximal face trilete, bearing spaced tubercles 7–11 per areole, 11.25–22.5 µm in diam., with dense threads in between, only a small apex free of waxes, ridges c. 50 µm wide and c. 20 µm high, almost free of waxes; distal face with spaced larger and smaller pustules, 30–45 µm in diam., partly anastomosing, c. 26.25 × 15 µm, with dense threads between pustules, large apex of pustules free of waxes. Microspores not seen.
Distribution — Known only from the type locality in the Rusizi plain of W Burundi (Fig. 14B). The above cited collections were already mentioned as Isoetes abyssinica Chiov. by Pichi Sermolli (1983, 1985).
Habitat — Amphibious, in seasonally waterlogged depressions in palm savanna, 780–850 m.
IUCN conservation assessment (preliminary) — Critically Endangered: CR B2ab(iii). Isoetes pichisermollii is known only from the type locality and its immediate surroundings. The last collections were made c. 50 years ago. The estimated AOO is 4 km2 (assuming a 4 km2 grid cell size). The habitat, a seasonally waterlogged depression in palm savanna, is under high pressure by agriculture (see Ntore & al. 2018). Because a part of the Rusizi plain is situated in eastern D. R. Congo, the species may well also occur in that country.
Etymology — Named after Rodolfo Emilio Guiseppe Pichi Sermolli (1912–2005), a famous Italian pteridologist, who first mentioned the taxon from Burundi.
Taxonomic notes —Verdcourt (2005: 3) stated, without having seen the spores, that “these Burundi specimens [of Isoetes abyssinica] seem too robust”. Isoetes abyssinica s.str. was placed into synonymy of I. welwitschii by Verdcourt (2005), but there are sufficient differences, e.g. in megaspore micromorphology, to keep both taxa as separate species. The specimen Reekmans 4400, which we have chosen as the holotype, bears a pencil annotation by Henk Beentje who identified it as I. schweinfurthii.
Additional specimens studied — Burundi: Bujumbura: vallée Mugegi, km 14, 13 Mar 1971, Reekmans 91 (BR0000015460400). — Bubanza: plaine de la Rusizi, 19 Feb 1971, Lewalle 5192 (BR0000013164775); plaine Rusizi km 14, 18 May 1974, Reekmans 3451 (BR0000015460424, K001291891).
Isoetes rwandensis Eb. Fisch. & Lobin, sp. nov. – Fig. 12–13, 14B.
Holotype: Rwanda, Eastern Province, Bugesera, Nyamata, 02°07′00.91″S, 30°04′07.67″E, 1415 m, seasonal shallow ponds on ferricretes, 9 Jan 2012, Fischer 66/2012 (BR0000015253576V).
Diagnosis — The new species differs from Isoetes abyssinica and I. welwitschii in the shorter leaves (55–62 mm vs 114–185 mm in I. abyssinica and 50–200 mm in I. welwitschii). It differs in the colour of the megasporangium wall (dark brownish to blackish vs pale in I. abyssinica and I. welwitschii). The megaspores are smaller (c. 400 × 400 µm vs c. 480 × 460–480 µm in I. abyssinica). The distal face is densely pustulate-tuberculate with larger, rounded pustules intermixed with smaller tubercles, sometimes anastomosing, whereas in I. abyssinica the distal face is clavate with distant projections and small tubercles in between, and I. welwitschii has a distal face with large pustules, partly anastomosing and with small tubercles intermixed.
Description — Corm 3-lobed, up to 5 mm wide, bud scales 2–2.5 × c. 1.5 mm, cuspidate, pale green. Leaves 15–21, 55–62 mm long, 1.2–1.6 mm wide at base, 0.4–0.6 mm wide at apex, tapering gradually to an acute apex. Ligule not seen. Velum absent. Megasporangia 2.2–2.6 × 1.2–1.4 mm, sporangium wall dark brownish to blackish. Megaspores c. 400 × 400 µm; proximal face trilete, evenly tuberculate with small and dense tubercles 28–30 µm in diam., ridges c. 50 µm wide and c. 33 µm high, areoles and ridges with dense threads; distal face densely pustulate-tuberculate with larger, rounded pustules 39.9–60 µm in diam. intermixed with smaller tubercles, sometimes anastomosing, up to 26 µm in diam., larger pustules sometimes anastomosing, dense threads between pustules, only apex of pustules ± free of waxes. Microspores not seen.
Distribution — Known only from the type locality and one additional locality in Eastern Province of Rwanda (Fig. 14B).
Habitat — In small, temporary pools on ferricretes (Fig. 12A) along with Callitriche oreophila Schotsman, Cyperus species, Lindernia parviflora (Roxb.) Haines, Mar-silea minuta L. and Rotala tenella (Guill. & Perr.) Hiern (see Fischer & Hinkel 1992).
IUCN conservation assessment (preliminary) — Critically Endangered: CR B2ab(iii). Isoetes rwandensis is now known only from one locality. The type locality near Nyamata was destroyed during road work in 2021 by covering the ferricrete with more than 1 m of soil. The estimated AOO is therefore 4 km2 (assuming a 4 km2 grid cell size). At the second location, there is a potential threat of house construction and road work.
Etymology — Named after the country of Rwanda, where the new species is probably endemic.
Additional specimens studied — Rwanda: Eastern Province: Mpanga, entrance of Ranch Mpanga between Lac Cyambwe and Lac Mpanga, 02°04′56.65″S, 30°46′39.96″E, 1310 m, seasonal shallow ponds on ferricretes, 30 Mar 1987, Fischer 110 (KOBL).
Discussion
The micromorphology of megaspores seems to be an important characteristic for species delimitation and, at least in the material available, is a ± constant feature for identification (see also Pereira & al. 2016, 2021). Together with the number of leaves and leaf size, it makes it possible to distinguish most of the Tropical African species. We studied the variability, e.g. in Isoetes schweinfurthii including the type, and found that the pattern of the pustulate distal face and the usually laevigate proximal face with no or only very few small tubercles occurs over the whole distribution area from Benin to South Sudan and Tanzania (see also the drawing in Crouch & al. 2011 and the SEM micrographs of I. kersii in Wanntorp 1970). On the other hand, there seems to be a considerable cryptic diversity and possibly more species involved in the material of Isoetes from Tropical Africa. Other characters like the velum or the lobes of the corm are often difficult to observe in herbarium specimens.
So far, only a few SEM micrographs of Isoetes megaspores from Tropical Africa have been published (e.g. Wanntorp 1970, who illustrated I. schweinfurthii [as I. kersii Wanntorp], or Schelpe & Anthony 1986, where the megaspores of I. aequinoctialis, I. schweinfurthii and I. welwitschii were illustrated). Here we provide the first SEM micrographs for I. abyssinica and I. alstonii. All taxa of Isoetes from Tropical Sub-Saharan Africa will be dealt with in a forthcoming revision.
Acknowledgements
We would particularly like to thank the Rwanda Development Board (RDB) for collection and export permits. We would also like to thank the BMUB (Federal Ministry for the Environment, Nature Conservation and Nuclear Safety) for funding the Project “Conservation of Biodiversity and Natural Resources and Climate Protection by sustainable Agriculture and Forestry at Cyamudongo Forest, Rwanda” (16_III_083_RWA_A_Cyamudongo Regenwald) within the International Climate Initiative (IKI) and the Akademie der Wissenschaften und Literatur Mainz for the financial support of field trips to Rwanda. Additionally we thank the curators of the herbaria B, BR, FT and K for making their collections accessible and for permission to study the megaspores. We also thank BR, FT and K for permission to reproduce images of specimens (Fig. 1, 8 and 10). Special thanks go to Maximilian Weigend, Nees Institute for Biodiversity of Plants, University of Bonn for permission to use the Scanning Electron Microscope and to Yaron Malkowsky for invaluable support during the photo sessions. We are most grateful to Dr Laura Tensen and Katie Price for correcting the English in our text. Finally, we would like to thank two anonymous reviewers for improving the manuscript.
