Checklist of Lycopodiopsida (clubmosses and quillworts) and Polypodiopsida (ferns) of Rwanda

Abstract: The checklist comprises 208 species and two varieties of Lycopodiopsida and Polypodiopsida. All historic literature records, mainly from Brause & Hieronymus (1910) and Pichi Sermolli (1983, 1985) have been revised. The pteridological results of 39 years of botanical exploration of the flora of Rwanda by Eberhard Fischer, have been added. Two new varieties (Pleopeltis macrocarpa var. dichotoma and P. macrocarpa var. pinnatiloba are validated. Citation: Fischer E. & Lobin W. 2024: Checklist of Lycopodiopsida (clubmosses and quillworts) and Polypodiopsida (ferns) of Rwanda. – Willdenowia 53: 149–172. Version of record first published online on 10 January 2024.


Introduction
The ferns and fern allies of Rwanda have received little attention.The only more detailed list providing localities was that by Pichi Sermolli (1983Sermolli ( , 1985)).Since then, only Roux (2009) published an updated list for all countries of Africa including Madagascar, albeit without reference to the single records.
During the preparation of an illustrated field guide of ferns and fern allies for Rwanda, including descriptions and keys for all taxa, the authors recorded numerous species as new country records and six species new to science, as well as two varieties previously not validly published.Two new species are already described, one in a paper on Isoetes in Central Africa (Fischer & Lobin 2022) and one Dryopteris species in a treatment of the exindusiate Dryo pteris species from Central Africa (Fischer & Lobin 2023a).A further three new Asplenium species and a synoptic revision of the genus in Rwanda, as well as an overview of Diplazium with the description of a new species, have recently been published (Fischer & Lobin 2023b, 2023c).
The aim of the present publication is to provide the first checklist of all fern and clubmosses species recorded for Rwanda and the formal description of Pleopeltis mac rocarpa var.dichotoma Eb. Fischer & Lobin and P. mac rocarpa var. pinnatiloba Eb. Fischer & Lobin.

Material and methods
The present checklist is based on an evaluation of the existing literature, herbarium studies in the following herbaria: B, BR, FI, K (abbreviations after Thiers 2022+), and fieldwork between 1984 and 2022.The authors have tried to verify all historic records, mainly from Brause (1910), Brause & Hieronymus (1910) and Pichi Sermolli (1983Sermolli ( , 1985)).

History of pteridological exploration of Rwanda
Until 1907, the flora and fauna of Rwanda were almost unknown to science.During the expedition of Graf von Götzen in 1894 (Götzen 1895) no ferns appear to have been collected in Rwanda, although he listed a few fern collections from the ascent of Mt Nyiragongo, part of the Virunga massif in eastern Democratic Republic of Congo (D. R. Congo).Richard Kandt (see Bindseil 2008), who lived in Rwanda as a private naturalist from [1898][1899][1900][1901][1902][1905][1906][1907], and later as the Imperial Resident for Rwanda until 1913, made some botanical collections, but only of flowering plants.In 1907 Adolf-Friedrich Her-zog zu Mecklenburg embarked on an expedition with the intention of exploring Rwanda and the eastern Belgian Congo.He was accompanied by the geologist Egon von Kirschstein, botanist Johannes Mildbraed, zoologist Hermann Schubotz, anthropologist Jan Czekanowski, Lieutenant and cartographer Max Weiss, physician and bacteriologist W. von Raven, as well as Lieutenant Walter von Wiese und Kaiserwaldau, Friedrich Weidemann, Sergeant Czeczatka and 25 Askari (Herzog zu Mecklenburg 1909).They travelled by train to Lake Victoria and trekked to northeastern Rwanda, where they collected at Lake Mohasi (see Bamps 1975).Having visited the court of King Yuhi V. Musinga at Niansa, Mildbraed and Schubotz left the expedition for about two weeks in order to collect plants and animals in the Nyungwe forest (= Rugege Wald).By March 1908, Mildbraed had visited Lake Kivu and the Virunga Volcanoes, followed by the eastern Congo (Ituri, Aruwimi) and the Ruwenzori mountains.In May 1908 the expedition party travelled down the river Congo by steamboat until they reached the western coast of Africa.They arrived in Hamburg on 30 th June 1908.The scientific results, including zoology, were not published until 1925.The botanical volume, edited by Mildbraed (1910) covered 718 pages.The ferns and fern allies were studied by Brause (1910), Brause & Hieronymus (1910) and Hieronymus (1910).The lycophytes were identified by Herter.The authors recognized 116 species collected during the expedition, among them 12 new species and one new variety.They recorded 47 species for Rwanda, five of them described as new (see Table 3).Their treatment would remain a classic work and, for almost 70 years, the only account for Rwanda and D. R. Congo (former Zaïre).
The next comprehensive work on the ferns was compiled by Pichi Sermolli (1983Sermolli ( , 1985)).He published an overview of the ferns of eastern D. R. Congo, Rwanda and Burundi.In these papers, he listed all available collections from the region, except those of Mildbraed, and the account is based on his own collections from 1956 and on those from researchers who mostly worked in the area between 1956 and 1982.Pichi Sermolli himself collected only for a few weeks in Rwanda, mainly in the Nyungwe Forest.But he included in his work many collections from various collectors.He described 15 new species, nine of them from Rwanda (see Table 3).In total, Pichi Sermolli recorded 112 species from Rwanda.He was aware of the outstanding botanical and zoological diversity of the region and stated that the Albertine Rift was poorly studied.
While a Flora for the seed plants of the Albert National Park (today Parc National des Virunga in D. R. Congo and Volcano National Park in Rwanda) was published by Robyns (1947Robyns ( , 1948) ) and Robyns & Tournay (1955), nothing was available for the ferns.In 1945 Taton produced a handwritten manuscript for the ferns of this national park, but it was never published (Bamps 1990).The French botanist H. Humbert was the first to collect on Mt Kahuzi and Mt Biéga in 1929, and also visited the Virunga volcanoes.A. R. Christiaensen, a private researcher associated with the Institut de Recherche Scientifique en Afrique Centrale (IRSAC), collected ferns in Rwanda between 1955 and 1957.
After the independence of Rwanda and D. R. Congo (then Zaïre), several botanists continued to work in this phytogeographically interesting region.From December 1971 to March 1972 and in 1974, the members of the "Mission des Volcans", P. H. Auquier, P. Bamps, J. E. J. Lambinon, and P. Van der Veken collected in the Nyungwe (= Rugege) Forest and on the volcanoes in Rwanda.They also made extensive collections on Mt Kahuzi, Mt Biéga and around the Irangi Station in D. R. Congo.G. Bouxin and M. Radoux collected in Akagera National Park between 1969and 1970, and G. Bouxin made collections of ferns between 1970and 1972 in Nyungwe Forest.During botanical explorations for the "Flore du Rwanda, Spermatophytes" (Troupin 1978, 1983, 1985, 1988), G. Troupin also collected ferns, mainly between 1956and 1982. Since 1969, single 1969d, Schizaeaceae: Lawalrée 1970).Only in the treatment of Selaginellaceae (Bizzari 1985) was a larger number of 23 taxa included.Therefore, until now a total of 74 fern species from Central Africa (D. R. Congo, Rwanda, Burundi) have been subject to taxonomic treatment.Kornaś & al. (1993) provided a distribution atlas of the ferns and fern allies of Rwanda based on the collections published by Pichi Sermolli (1983Sermolli ( , 1985) ) and those of K. A. Nowak.The latter, a priest, lived in Rwanda from 1978 to 1984 and collected ferns in his spare time over almost all Rwanda (Kornaś & Nowak 1991).Seven species were mentioned for the first time for Rwanda.The majority of his specimens are deposited in Krakow (KRA) with duplicates in Meise (BR).Dzwonko & Kornaś (1994) analysed the distribution patterns and diversity of Rwandan ferns.
From 1984 to 2022 the first author (EF) studied the flora and vegetation of Rwanda and eastern D. R. Congo.He was among the first to collect in remote sites and botanically undercollected regions (e.g.Cyamudongo Forest, Busaga Forest, Kagitumba, Ibanda Makera etc.).He found 39 taxa for the first time in Rwanda, among them six species (see Table 3).24 species are recorded for the first time in this checklist.The other 10 new records and the six new species have been published elsewhere.1).
The picture is quite different if we look at the species/ area ratio.From this perspective, top of the list are the small islands of São Tomé with 128 species in 17 km² and a species/area ratio of 7.52941.Then come Annobón with 40 species in 17 km² and a species/area ratio of 2.35294, Principe with 64 species in 136 km² and a ratio of 0.47059, Bioko with 214 species in 2017 km² and a ratio of 0.10610, and the Cape Verde islands with 36 species in 4033 km² and a ratio of 0.00893.Rwanda with 208 species and a surface area of 26,338 km² is ranked at place six with a ratio of 0.00790 (Table 1).The large and diverse countries like Tanzania with 423 species and an area of 945,087 km² and the D. R. Congo with 314 species and a surface of 2,345,409 km² have only a ratio of 0.00045 and 0.00013, respectively.However, the high species number recognized for Rwanda is certainly the result of intensive collecting during the last three years, and Burundi and the eastern D. R. Congo probably harbour many species not yet recorded.
The complete absence of neophytic fern species is remarkable.The taxa known as neophytes in other parts of the World are the following: Azolla filiculoides Lam. is known from Morocco and southern Africa and has no natural occurrence on the African continent.The species has not yet been recorded for Rwanda.Nephrolepis bi serrata Schott is frequently cultivated in Rwanda but there is no occurrence outside gardens.However, it has its natural distribution in all neighbouring countries.Other potential neophytes like Selaginella kraussiana (Kunze) A. Br., Christella dentata (Forssk.)Brownsey & Jermy and Pteris vittata L have already been collected by Mildbraed in 1907 and occur in their natural distribution area.Pteridium aquilinum (L.) Kuhn is represented by the African subsp.capense, and its huge stands are already described by Mildbraed (1910) as "Pteridium-Formation".
The number of Albertine Rift endemics and local endemics is considerably high in Rwanda.The Albertine Rift, as defined by Plumptre & al. (2007), includes much of the western Rift valley down to southern Tanzania and northern Zambia.We define it as the region from Lake Albert to the southern tip of Lake Tanganyika.Examples of important forest areas are Budongo Forest, Kibale NP, Ruwenzori, the Virunga Massif, Nyungwe and Kibira NP, Bururi Forest, Kahuzi-Biéga NP, Itombwe Massif, Mt Kabobo, Mahale Mts.NP, and the Marungu Plateau (Plumptre & al. 2007).
From the 208 species of ferns and fern allies recorded from Rwanda, 20 species are Albertine Rift endemics, present at least in Rwanda and eastern D. R. Congo or Burundi (Table 2), and eight species are local endemics, currently only known from Rwanda (Table 2).Therefore, 28 endemic species are recorded that represent 13.46% of the total fern flora.
If we compare the number of endemic species, Rwanda is ranked at number four after South Africa, which has 50 endemic species (mainly in Isoetes and Cheilanthes), Tanzania with 33 species and D. R. Congo with 31.Concerning the percentage of endemics for the whole fern flora, Rwanda with 13.46% ranks third after South Africa with 16.8% and Namibia with 13.5 %, and is followed by São Tomé and Annobón, each with 10%, and D. R. Congo with 9.8% (Table 1, 2).A list of all range-restricted ferns and fern-allies from continental Africa is provided in Supplementary table S1 (see Supplemental content online).

Checklist
The taxa are arranged in systematic order after PPG (2016), and Wei & Zhang (2022).For the first records, we cite the name under which the relevant author published it.Misidentifications are recognizable by "auct.non", synonyms bear full authors citations.New records for Rwanda are marked with "+" before the species name.
The Checklist contains 208 species and two varieties.The most species-rich fern-genus in Rwanda is Aspleni um with 44 species (almost every fifth species is an As plenium), followed by Pteris (11 species) and Dryopteris (10 species out of 26 recorded by Roux (2012) for the whole African continent).
In Rwanda the exploration of the pteridological flora had three major periods: at the beginning of the 20 th century, culminating with the collections from Mildbraed (Mildbraed 1910), a second period in the 1950s with the main collector Pichi Sermolli (Pichi Sermolli 1983, 1985), and a third, from 1984 until today mainly with the collec-tions from the first author, Eberhard Fischer.An enumeration of the number of species mentioned by the above cited collectors for the first time for Rwanda is found in Table 3.
All Pteridium specimens from Meise (BR) collected in Rwanda, three of which were misidentified as Pteri dium aquilinum var.africanum (Bonap.)R. M. Tryon (= P. centraliafricanum), are P. aquilinum subsp.capense.The latter taxon is found in montane forests on open ground and clearings, while P. centraliafricanum is restricted to grassland and dry forests.
+Lastreopsis vogelii (Hook.)Tindale New record -Rwanda: Northern Province: Kinigi, 25 Jun 1961, S. C. Antun Gupfert 1005 (BR0000017581714!).Note -This specimen was deposited in BR as Lastre opsis sp.It has never been determined and published, and the species is not recorded for Rwanda in the checklist of Roux (2009).We searched for the species at Kinigi without success.

Trichomanes crispiforme Alston
Note -This taxon was described from São Tome and represents a West African element.It is only known from Liberia, Nigeria, Cameroun, São Tome, Congo (Brazzaville), and D. R. Congo.The locality that is closest to the border of Rwanda is Irangi N of Kahuzi-Biéga National Park (Kornaś 1994).Roux (2009: 48) listed Rwanda among the recorded countries without mentioning a source.This record is considered here as erroneous.

Taxonomic treatment
Hieronymus in Brause & Hieronymus (1910) mus (1910) gave no descriptions and therefore published nomina nuda, but as he placed his name behind the varieties, he certainly regarded them as new to science.We therefore decided to validate them (see below).
In his treatment of Polypodiaceae for the Flora of Tropical East Africa, Verdcourt (2001: 28) assigns a "mutation" to some collections from Uganda and Kenya, citing Schelpe & Anthony (1986) who discussed these forms.In South Africa, Pleopeltis ×simiana (Schelpe & N. C. Anthony) N. R. Crouch & Klopper is considered to be a natural hybrid between P. macrocarpa and P. polypodioides subsp.ecklonii (Kunze) J. P. Roux.This hybrid looks quite similar to the East African plants and to our material from Rwanda.Verdcourt (2001) already points out that these specimens occur far from the natural range of P. polypodioides subsp.ecklonii (SE Tanzania, Mozambique, Malawi, S Africa) and the plants from Rwanda have, as do the three examined specimens in Flora of Tropical East Africa, normal rather than abortive spores (Verdcourt 2001).Therefore, we propose, that these specimens merit recognition as separate taxa.
Similar forms with pinnatilobed fronds have been recently described as new species from eastern D. R. Congo.Loxogramme ntahobavakiana Mangambu Mokoso & van Diggelen (2017: 64) differs from L. abyssinica mainly in the pinnatilobed leaves.Lepisorus robbrech tianus Mangambu Mokoso & van Diggelen (2017: 65) is separated from L. schraderi mainly by the presence of long and dichotomously lobed leaves.However, we prefer to keep the material from Pleopeltis macrocarpa forms from eastern D. R. Congo and Rwanda in the rank of varieties.

Table 1 .
Species number, species/area ratio and endemics of clubmosses, quillworts and ferns of continental African countries (including Cape Verde and islands of Gulf of Guinea).
Roux (2009)rdcourt's taxonomic  view (2003)and listed "subspecies B" from Algeria, Morocco, Cameroon, Sudan, Ethiopia, Uganda, Kenya, Lesotho and South Africa.All records probably belong to C. diaphana but need verification by spore characters.According toRoux (2009), this species is known only from the Comoro Islands and Réunion.The author also erroneously placed C. viridula as a synonym of C. fragilis.Here we provide the first definite record of C. diaphana for Central Africa.