New records and key to Poa (Pooideae, Poaceae) from the Flora of Southern Africa region and notes on taxa including a diclinous breeding system in Poa binata

Abstract Four species of Poa L. are newly reported for sub-Saharan Africa and southern Africa, Poa compressa L., P. iconia Azn., P. infirma Kunth and P. nemoralis L. This is the first report of P. iconia from Africa. Vouchers at PRE of P. bulbosa L. all belong to var. vivipara Koeler, those of P. iconia belong to var. iconia and the one of P. trivialis L. belongs to var. trivialis. Two subspecies are recognised in P. pratensis L.: subsp. irrigata (Lindm.) H.Lindb. and subsp. pratensis. We also designate a lectotype for P. iconia and second-step lectotype for P. leptoclada Hochst. ex A.Rich. and report the first recording of a diclinous breeding system in P. binata Nees. Our account updates the treatment in Identification Guide to Southern African Grasses (Fish et al. 2015) including a key to the taxa and notes on infrageneric taxonomy, DNA subtypes, ecology, chromosome numbers and breeding systems.


Introduction
The genus Poa L. includes over 580 species (RJS count 2020) and occurs on all continents. In Africa, 38 species are reported (Valdés and Scholz 2009;Clayton et al. 2016; Plants of the World Online 2020), 14 of which extend to Africa from their primary distributions in Europe and/or Southwest Asia. Twenty-four species are endemic. Of the endemics, eight are confined to northwest Africa (Libya westwards), nine to Ethiopia and Eritrea (Phillips 1995), three to Madagascar and one to the Canary Islands. Of the five endemic or indigenous to Africa in Tropical East Africa (Clayton and Renvoize 1982), P. schimperiana Hochst. ex A. Rich. and P. leptoclada Hochst. ex A. Rich. are more wide ranging in eastern Africa (both reaching the Arabian Peninsula) and P. leptoclada is reported from the Canary Islands (Valdés and Scholz 2009; although RJS thinks those specimens represent P. flaccidula Boiss. & Reut.; RJS pers. obs.). In the Flora of Southern Africa region (Botswana, Lesotho, Namibia, South Africa and Eswatini a.k.a. Swaziland; FSA), Fish et al. (2015) recorded six species of Poa, four of which are introduced from the temperate northern hemisphere (P. annua L., P. bulbosa L., P. pratensis L. and P. trivialis L. without noting any infraspecies) and none of which is endemic to the FSA (P. binata Nees near-endemic to the FSA being also found in Zimbabwe). Poa binata and P. leptoclada are the only indigenous species.
There is a strong association of FSA Poa with southern Africa's mountains: three species are closely aligned in distribution with the rugged, moist eastern Escarpment (P. annua, P. binata and P. leptoclada); one with the eastern Escarpment and Cape Flora (P. pratensis) and one with arid western Escarpment (P. bulbosa var. vivipara Koeler). Poa leptoclada, in the FSA region only known from a few collections from the Maloti-Drakensberg (MD), also occurs naturally in the eastern African mountains and into Yemen (Fish et al. 2015).
Although the FSA Poaceae flora is relatively well known, the grass flora of the MD remains incompletely known, especially in more poorly-botanised areas, such as the Eastern Cape Drakensberg (including the former Transkei) and the alpine zone across the MD (Pooley E, pers. comm.). Given the immense grazing pressure that the MD is under from communal rangeland use and associated ecological degradation, it is imperative that the taxonomic status of these natural montane rangelands -where they still exist -are carefully documented. In addition, the FSA region still has many questions and complexities as to the accurate identity and taxonomic status of mountain-associated genera, such as Festuca L. (Sylvester et al. in press), Trisetopsis Röser & A. Wölk (our species included in Helichtotrichon Besser by Fish et al. 2015, revised Trisetopsis by Mashau et al. 2020), Poa and others; these temperate, usually C 3 groups, are essential components in the functional ecology of these mountains as indigenous pastures, particularly in the alpine zone of the MD.
From February-March 2020, a comprehensive survey of MD Poaceae in the alpine zone was undertaken by SPS, MDVPS and RJS. During fieldwork, two previously-unreported species of Poa were recorded for the FSA region (Fish et al. (2015): Poa compressa L. and P. nemoralis L. In addition, while identifying the grass collections at the South African National Herbarium in Pretoria (PRE), three additional collections of P. compressa and two more introduced species of Poa (P. iconia Azn. (var. iconia) and P. infirma Kunth) were discovered amongst herbarium collections. Infraspecific determinations of certain taxa were also made for the first time, with P. bulbosa identified to var. vivipara, P. pratensis identified to subsp. irrigata (Lindm.) H.Lindb. and subsp. pratensis and P. trivialis identified to subsp. trivialis.
Accordingly, here we present: 1. Details on these new records to FSA; 2. An updated key for the Poa of the FSA region; 3. Taxonomic notes on Poa of the FSA region, including reporting a diclinous breeding system in P. binata. Aside from P. trivialis L., which was reported to be selfincompatible and sexually reproducing (Connor 1979), the other introduced species are either inbreeders or known for apomictic reproduction.

Materials and methods
Extensive field collecting was conducted by SPS, RJS and MDPVS throughout the MD between 1 Feb and 9 Mar 2020, with specimens deposited in the US [first set, pending export permits], PRE and NU herbaria (Herbarium acronyms follow Thiers [continuously updated]). Study was also conducted at the PRE herbarium between 13 and 20 Mar 2020. Visits to other national herbaria in southern Africa (e.g. NU) were not possible due to the onset of the Covid-19 pandemic. We follow Fish et al. (2015) for country and province distributions and only report vouchers renamed at PRE to the newly-reported species and those of our new collections of Poa from the MD. Collection records used to plot species dot maps in Fish et al. (2015) are available online from SANBI (South African National Biodiversity Institute) -PRECIS (National Herbarium Pretoria [PRE] Computerized Information System) which covers NBG, PRE and UDW herbaria; http://www.sanbi.org. These data are also reflected by GBIF; http://www.gbif.org.

Taxonomic treatment
New FSA records Four new species records are presented for the FSA: Poa compressa, P. iconia var. iconia, P. infirma and P. nemoralis. New infraspecific records are also presented for the FSA, with P. trivialis identified to subsp. trivialis, P. bulbosa identified to var. vivipara and two subspecies are recognised in P. pratensis: subsp. irrigata and subsp. pratensis.

Key to Poa in the Flora of Southern Africa region
The following presents a key to all the Poa species and infraspecies that are currently known to occur in the FSA region. 'Glabrous' means without pubescence, 'smooth' means without prickle hairs/hooks. Leaf blades of two forms, vegetative blades slender and elongated, ca. 0.5-1 mm wide as folded or involute, culm blades shorter and broader and flatter; collars and sheaths usually glabrous; first glume 1-or 3-veined ..... P. pratensis subsp. pratensis (if the lateral shoots occur in tight, intravaginally originating fascicles and the blades are fairly firm (with veins pronounced abaxially, strigulose hairs common adaxially), the plants belong to P. pratensis subsp. angustifolia [L.] Lej.)

Taxon notes
For full explanation of genotype coding in Poa, see Soreng et al. (2010Soreng et al. ( , 2020. For genotypes, the first letter indicates the plastid clade and the second letter the nuclear ribosomal internal and external transcribed spacer clade. The 2n chromosome number modes are in italic, main modes are bold. Notes. Poa annua is a tetraploid species derived from hybridisation, somewhere around the Mediterranean Sea, between two diploids that overlap in that region: P. infirma (maternal parent, contributor of the plastid genotype) and P. supina Schrad. (paternal parent, providing the nuclear ribosomal internal [and also external] transcribed spacer genotypes) (Soreng et al. 2010). It is sometimes considered the world's most widespread weed. Poa annua grades in form in the directions of both parents, sometimes making it tricky to differentiate, especially from P. infirma. Hybrids with P. supina, called P. × nannfeldtii (H. Scholz ex Val.N.Tikhom.) Nosov, exhibit a C-value indicative of triploidy (Soreng, pers. obs.). Self-compatible, mostly inbreeding, it is gynomonoecious. The upper florets within spikelets being pistillate facilitates outcrossing. 2n = 28. -M i m u genotype.   Notes. Poa binata is a common species in the upper Maloti-Drakensberg mountains. In areas with enough moisture and low grazing pressure, the species can be the dominant grass species, forming dense tussocks to 0.5 m diameter. As in many large grass tussocks, a few shoots can appear to be rhizomatous, but are actually stooling shoots as in P. bidentata (see below). Under high grazing pressure, plants become smaller and weaker and sparsely distributed. Plants seem to tolerate burning well. The species displays unusual diversity in lemma pubescence, varying from glabrous to pubescent on three veins, to pubescent on five veins and sometimes between veins and callus hairs may be present or absent. Flowers are pistillate and/or perfect within plants, anthers are 1.5-2.7 mm long or vestigial. 2n = 28, 42, 56. -HA genotype (Gillespie and Soreng, unpublished).

Poa binata
The species exhibits a diclinous breeding system. Most species of Poa are hermaphroditic. Dicliny occurs in about one quarter of the species of Poa examined and ranges from simple gynomonoecy to full dioecy ). In P. binata, many plants have spikelets with pistillate upper flowers. Other plants exhibit more pistillate flowers within spikelets and wholly pistillate spikelets. The latter are concentrated on the lower branches of panicles. Some plants were judged to be completely pistillate. The sterile rudiments of anthers (staminodes), present in pistillate flowers, are believed to result from genetic control, not from apomixis. All other florets, spikelets and sometimes whole plants examined were perfect-flowered. The breeding system of P. binata needs further study, but seems to match sequential gynomonoecy as described by Soreng and Keil (2003). This breeding system is estimated by RJS to occur in 28 species equally divided between the Americas and east Asia , almost all of which have anthers averaging 2 mm long or longer.
The lectotype at P is selected as it is one of two sheets with Drège's original handwritten location and date, the other original set of tickets being destroyed (Gunn and Codd 1981). The lectotype is clearly distinct from all the others, which may or may not be duplicates of the second collection cited by Nees ab Esenbeck (1841). Other syntypes or original material have only secondary notes from Ernst Meyer's distribution of Drège sets (in 1837, 1840, 1847Meyer 1837Meyer , 1840Meyer , 1847 or guessed at from other duplicates, some of which may actually have been collected by Zeyer (who joined the Drège brothers in 28 Nov 1832 into early December and then collected on his own for some months before departing South Africa, for example, the K000345193 sheet which originally said Zeyer, but that was crossed out and replaced by Dredge and a location where they collected together). For further reading, see Gunn and Codd (1981 Poa bidentata Nees is usually placed in P. pratensis, but in our opinion, it is merely a stooling example of P. binata. It has lemmas that, in addition to having pubescence like P. pratensis, are quite scabrous in the margins and between the veins, ruling out P. pratensis. There are various sheets and fragments of P. atherstonei (= P. binata) at PRE, collected by Ms. Pelger between 1901 and 1914, but only one that matches the date and cited by Hackel (1904) . That one has lemmas that are glabrous or sparsely pubescent on the keel and marginal veins, web short and scant or absent. Distribution. native to Eurasia and northwest Africa. Introduced/possibly arrived via long-distance-dispersal, but that seems unlikely for the bulbils are bulky and have no special dispersal mechanisms.

Poa bulbosa
Ecology. hemicryptophyte, geophyte, with bulbous based shoots that store hemicellulose. Well-adapted to temperate climates with winter rains and dry summers.
Flowering. winter and spring green, flowering in mid-spring and quickly going dormant, flowers mostly forming bulbils. Apomictic.
Economics. common, excellent early spring forage for sheep, but invasive and can become dominant.
Vouchers. no new records. Notes. All the specimens reviewed at PRE were pseudoviviparous, at least in part. More or less normal-looking lemmas are commonly present in the lower one or two florets of bulbiferous spikelets. The very normal-looking lemmas will have soft hairs on the keel and marginal veins and a tuft of longer hairs on the dorsal side of the callus. The normal florets are thought to be fertile to some degree, although RJS has rarely observed seed in these. Some plants produce more normal florets and more normal spikelets than others, but the main mode of dispersal and establishment is by leafy bulbils that readily root and grow with the next seasons' rains. Some taxonomists decline to recognise infraspecies here, but for purposes of natural history research, it is useful to identify plants with any bulbiferous spikelets as var. vivipara. Apomictic via bulbifery. 2n = 21,28,29,31,32,33,34,35,37,42,44,46,48,49 Notes. First reports for South Africa and Lesotho. Apparently, it is well established in the southern Drakensberg, where it was collected previously in 1959 and three times   Notes. First report for the African continent and South Africa and Lesotho. Poa iconia was recognised as Poa pelasgis H. Scholz (Scholz 1985), a synonym of Poa iconia var. pelasgis (H. Scholz) Soreng (Soreng and Simmons 2018), its normal-flowered counterpart. The species genotype markers suggest it is only remotely related to P. bulbosa (Cabi et al. 2016). Aznavour (1918) did not state a collection number or herbarium. Only three sheets have been located that match the protologue, all Post B 53 (the E sheet originally had B29, but that was crossed out and replaced by 53), all three are viviparous. We select the E sheet where Aznavour's herbarium and types are kept as the lectotype. Apomictic via bulbifery. 2n = unknown (possibly, in a few cases, counted as P. bulbosa var. vivipara.) -Nn genotype (Cabi et al. 2016).  Ecology. wet places in high Maloti-Drakensberg.

Poa infirma
Flowering. around July. Economics. rare, insignificant. Vouchers. no new records. Notes. Poa leptoclada exhibits a wide variation in floret pubescence. Callus hairs may be present or absent and lemma hairs, when present, occur on the keel only, the keel and marginal veins and sometimes between them. Infrequently, florets are entirely glabrous and callus and lemma hairs occur in different combinations of presence and absence. We did not have time to evaluate the case in Drakensberg plants. Presumably it is self-compatible and mostly self-fertilising. Clayton (1970: 47) incompletely lectotypified P. leptoclada on a Schimper 1826 TUB collection, although without mentioning which specimen or leaving annotations on any of the three duplicates at TUB. We second-step lectotypify to the TUB009107 collection as this is presumably the sheet Clayton (1970) considered as "holotype", as it is the only sheet which displayed Hochstetter's handwritten diagnosis and was photographed for K (K negative No. 10325, 23 Sep 1968). 2n = 28, 42. -Hh genotype (Gillespie and Soreng, unpublished).
Ecology. ruderal of temperate climates.  Notes. Poa trivialis subsp. trivialis is reputedly self-incompatible and sexually reproducing (Connor 1979). It can be quite invasive in temperate climates with a cool wet season. Aesthetically, it makes a poor lawn grass due to its sprawling habit when mown. Valdés and Scholz (2009) recorded it only for Algeria in North Africa. The second major subspecies, P. t. subsp. sylvicola (Guss.) H. Lindb., has bead-like swellings along the stolons and more hair on the lemma marginal veins and is more tolerant of drought: It is infrequently found outside of the Mediterranean basin and Irano-Turainian floristic region, but is reported across northern Africa (Valdés and Scholz 2009). 2n = 14, 14 + 1 -2B, 15, 27, 28 (27 and 28 counts not confirmed to subspecies may represent subsp. sylvicola). -Vv genotype. discussions of taxa, herbarium sheet images and supplying collecting paper; Anthony Mapaura for assistance in the field; Mary Namaganda and Muthama Musaya for helpful reviews; Nicky and Mark McLeod and AfriSki for logistical assistance in Lesotho; and Ralph and Nadine Clark for providing an operations base in South Africa (including during lockdown for SPS and MDPVS). We also wish to extend grateful thanks to the permitting authorities and landowners for the relevant permits and permissions to undertake the fieldwork: