Saxicolella Engl.
Creators: name: Cheek, Martin
name: Molmou, Denise
name: Magassouba, Sekou
name: Ghogue, Jean-Paul
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Malpighiales
Podostemaceae
Saxicolella

description: <b>Saxicolella</b> <i>Engl.</i> (Engler 1926: 356), non J.B. Hall (1971: 122); non Ameka <i>et al.</i> (2002). Type species: <i>Sapicolella nana</i> Engl. <i>Pohliella sensu</i> Taylor <i>quoad</i> <i>P</i>. <i>flabellata</i> (Taylor 1952: 52). Heterotypic synonym. <i>Rheophytic herbs. Roots</i> ribbon-like and/or disc-like, crustose, highly dorsiventrally flattened, to at least five times as wide as thick, adhering to the substrate by root hairs on the ventral surface, rootcaps and haptera absent. <i>Shoots</i> erect, minute and supporting sessile leaf rosettes, the stem then not visible, then arising from the margins of the radiating ribbon-like part of the root or, (<i>S. futa</i>) the sinuses of the bifurcations of the ribbon-like root OR up to several cm long, unbranched or branched, arising from either the centre of the disc-like crustose part of the root. <i>Leaves</i> with spiral phyllotaxy, bases sheathing where known, with one or a pair of acute basal stipules in leaves subtending spathellae (stipules absent in <i>S. futa</i> and often in proximal leaves on a stem of other species), blades filiform or flattened, usually entire, rarely bifurcate (or trifurcate) in <i>S. flabellata</i> and <i>S. nana</i> respectively, blades reduced or rudimentary in <i>S. deniseae</i> and <i>S. marginalis</i> or absent in <i>S. futa</i>. <i>Flowers</i> single, terminal on shoots, rarely in clusters on main stem (<i>S. angola, S. flabellata</i>). <i>Spathellae</i> ellipsoid, sessile, rarely globose (<i>S. ijim</i>), apex often with mucro. Flowers erect in intact spathellum, held completely partly within the opened spathellum at anthesis except in <i>S. nana</i> and <i>S.</i> sp. A. Pedicel accrescent in fruit. Tepals 2, filiform rarely spatulate (sometimes spatulate in <i>S. ijim</i>), flanking the stamen. Stamen single, exceeding ovary, thecae often divergent. Pollen in dyads. Gynophore present (except <i>S.</i> sp. Aand <i>S. ijim</i>). Ovary unilocular, ellipsoid, not laterally compressed, isolobous, erect, 6 or 8- ribbed in fruit, ovules numerous around a columnar axil placenta, septum not detected. Stigmas 2, botuliform to filiform or complanate. <i>Fruit</i> dehiscing into two equal, persistent valves. <i>Seeds</i> ellipsoid, mucilaginous. Discovery The first published and type species of <i>Sapicolella, S. nana</i>, was collected in Kamerun, then a German colony, now Cameroon, in January 1913 by the renowned botanist Mildbraed (Engler 1926). In 1922 Gossweiler in Angola first collected material of the species published in this paper as <i>S. angola</i> Cheek. Keay, collecting in eastern Nigeria in 1938 and 1950, made the specimens that became the basis of <i>S. flabellata</i> (G.Taylor) C.Cusset (originally published as <i>Pohliella)</i>, and <i>S. marginalis</i> (G.Taylor) C.Cusset ex Cheek (originally published as the monotypic <i>Butumia</i>). In 1998 the first author collected in Cameroon and misidentified as <i>Ledermaniella</i> cf <i>musciformis</i> the species published in this paper as <i>S. ijim</i> Cheek. Then, in Guinea-Conakry in Jan. 2018 he collected the material of the species named here as <i>S. futa</i> Cheek sp. nov., together with the second author. The second and third authors then went on in Feb. 2018 to collect the species described as <i>S. deniseae</i> Cheek sp. nov. <i>Sapicolella</i> sp. Aonly came to our attention as this paper was being concluded in mid- 2021, thanks to photos via GBIF.org of recent collections by the LBV-MO botanical team. The new species published in this paper are unlikely to be the last added to the genus. It is expected that botanical survey of the many rapids and waterfalls of Africa that have never been inspected for Podostemaceae will produce additional species new to science if this can be done before they are modified by the hydro-electric projects which are likely to result in their extinction. Morphology While species of several other genera of African Podostemaceae have been investigated in detail for their morphology and anatomy in such studies as Moline <i>et al.</i> (2007) and Thiv <i>et al.</i> (2009), this has not been the case for any of the species of the genus <i>Sapicolella</i> Engl. as delimited here (the Ghanaian species previously referred to as <i>Sapicolella</i> have been transferred to <i>Pohliella,</i> see Cheek 2020). None of the species appear to have been investigated anatomically, nor has their micromorphology been investigated under the electron microscope. The overview present- ed here is partly based on the protologues of the species already published by Engler (1926) &amp; Taylor (1952), but mainly from the observations of the authors of the four new species described below. <b>Root.</b> The root (thallus) is either crustose and/or with several, ± broadly ribbon-like arms radiating from a central crustose area (rarely absent/not detected e.g. <i>Sapicolella futa</i>). It is usually several times wider than thick, and is closely appressed to the substrate of smooth rock to which is firmly fastened by numerous short root hairs. A faint raised ridge running along the midline of the rootribbon of <i>S. futa</i> suggests that as in <i>Inversodicraea</i> (Cheek <i>et al.</i> 2017b), a single, central vascular bundle is present. Photosynthesis seems to be mainly performed by the ribbon-like roots since these make up most of the surface area of the plants, in fact&gt;90% of the area in almost all species. Root-caps have not been reported nor observed, but are in any case not usual in those Podostemaceae genera with crustose and broad ribbon-like roots. Nor are haptera, also known as hold-fasts, present. Roots are neither recorded nor preserved in the available material of <i>S. angola</i>, and are incompletely known in <i>S. nana</i> and <i>S. flabellata</i>. The ribbon-like roots of individuals appear to radiate out from the central point of establishment, presumably where a seed has germinated and established. In contrast, in <i>S. nana</i> the radial growth appears to be “crustose”, that is, not in the form of distinct separate ribbon-like structures, but a solid mass which extends outwards more or less evenly along the circumference, with only slight lobing at the margins. In most species, e.g. <i>Sapicolella deniseae</i>, and <i>S. marginalis,</i> the root is intermediate: it has both a central crustose part several centimetres in diameter, but also the margins are well-developed into radiating ribbon-roots. In <i>S. futa</i> the central crustose part if developed at all, must be small and only a short-lived stage which is lost by fruiting time (if it is developed in the first place), leaving the radiating roots disconnect- ed from each other at the centre. In most species the ribbon-like, radiating roots rarely (<i>Sapicolella deniseae, S. marginalis</i> and <i>S. ijim</i>) branch, when they bifurcate into two equal branches. However, in <i>S. futa</i> the branching is frequent and regular and the roots form a distinctive pattern. In fact, each species of <i>Sapicolella</i> can be identified by the architecture and grossmorphology of its root alone (where known), although this can be difficult to convey in words. <b>Shoots.</b> The origins of the shoots from the roots and their development, follows one of three patterns: 1. the shoots arise only from the central, more or less disc-like, crustose part of the root, and not from the radiating ribbon-like roots. The shoots form visible stems with measurable internodes. <i>Sapicolella nana, S. flabellata, S. ijim</i> and, possibly, (root unknown but visible stems present) <i>S. angola.</i> 2. The shoots arise only from the margins of the radiating, ribbon-like roots. The shoots are sessile, not forming visible stems but supporting an inconspicuous rosette of reduced leaves and a terminal spathellum. <i>Sapicolella marginalis, S. deniseae, S.</i> sp. A 2. The shoots arise only from the synusiae of the bifurcations of the radiating, ribbon-like roots. As in 2, the shoots are sessile, not forming visible stems. <i>Sapicolella futa.</i> These three shoot position patterns appear to have value in supporting generic delimitation in Asian podostemoids (Koi <i>et al.</i> 2012: 375), pattern 1=”D” (dorsal surface of root)”; pattern 2=”P (<i>Paracladopus</i> - type)”; pattern 2=”C (<i>Cladopus</i> -type)”; (Koi <i>et al.</i> 2012). The shoot patterns appear to correlate with the three root patterns (see Roots, above). The taxonomic significance is discussed below. In those species where visible stems are developed, they are erect, terete, and in those species where they exceed more than 5 mm long, sparingly branched. In <i>Sapicolella ijim</i>, the stems are robust and free-standing at anthesis. This species was found in the spray zone of a waterfall (Cheek pers. obs.) and is not supported by water as appears to be the case of the more laxly stemmed <i>S. flabellata</i> which has the longest (21 cm) stems in the genus, described as flowing in the protologue (Taylor 1952). <b>Leaves.</b> The phyllotaxy is consistently spiral. The leaves are best developed in the species with pattern 1 shoot position, where visible stems are developed. The largest leaves are those of <i>Sapicolella flabellata</i> which are flabellate (dorsiventrally flattened with radiating lobes) and up to 2 cm long, 2 cm wide. Each leaf bifurcates or trifurcates up to four times, the ultimate segments are capillary. The base is sheathing. Stipules are inconspicuous. Leaves in <i>Sapicolella angola</i> are poorly preserved, smaller, but otherwise similar, with fewer bifurcations and with stipules conspicuous. In <i>S. nana</i> the leaves are filiform-capillary and trifurcate, while those of <i>S. ijim</i> are unbranched and laterally compressed. In pattern 2 species, <i>Sapicolella marginalis</i> and <i>S. deniseae,</i> whilst the shoots are reduced and visible stems are not formed, the leaves appear reduced to the sheathing, stipulate base with only a rudimentary blade, while in <i>S.</i> sp. A, the linear blade is as long as the flower In pattern 2 <i>Sapicolella futa</i>, the leaves are reduced further, to inconspicuous, minute 0.2 mm long concave sheaths with stipules and blade not developed. Leaves of the type usual in African podostemoids are absent — that is, those which are filiform, terete and bifurcate repeatedly in the distal half, and which are shed before anthesis. <b>Inflorescences.</b> In all species flowers occur singly at the apex of shoots except in <i>Sapicolella flabellata</i> and <i>S. angola</i> where they are in terminal clusters. The developing spathellae are protected by the subtending leaves in the earliest stages. In fact, the leaves appear to function primarily as protective bracts in most of the remaining species of the genus. The spathellum varies from globose (<i>S. ijim</i>) to narrowly ellipsoid, sometimes with a small apiculus. It lacks a distinct stipe. <b>The flower</b> is erect and held within the opened spathellum at anthesis. Generally, only the styles and anthers are exserted from the ruptured spathellum but sometimes all or part of the ovary is projected from the spathellum. However, in <i>Sapicolella nana</i> and <i>S.</i> sp. A. the ovary can be projected on a naked pedicel as long as itself. Ashort pedicel, two filiform (rarely spatulate) tepals that flank the single stamen, and a short gynophore are present (absent in <i>Sapicolella</i> sp. A), all concealed within the ruptured spathellum at anthesis. The anther-thecae often face away from each other (latrorse). Pollen is dyad (where available for study). The ovary is either ellipsoid, e.g. <i>Sapicolella ijim, S. futa, S. marginalis</i>, or narrowly ellipsoid (<i>S. flabellata, S. deniseae, S. nana, S. angola, S.</i> sp. A). In the fruit there are eight longitudinal ribs extending from base to apex (<i>S. flabellata, S. marginalis, S. deniseae</i>) or the commissural ribs are not developed, when only 6 ribs are developed (<i>S. angola, S. nana, S. futa, S.ijim</i>). The two stigmas are filiform or narrowly botuliform (<i>Sapicolella nana, S.</i> sp. A, <i>S. angola, S. flabellata, S. deniseae</i>) or they are complanate (flat) and about as broad as long (<i>S. futa, S. marginalis, S. ijim</i>). The free-central axile placenta in the unilocular ovary is either narrowly spindle-shaped e.g. <i>Sapicolella angola, S. nana, S. futa</i> or broadly so, occupying about half the radius of the locular cavity in <i>S. ijim</i>. The seeds are all ellipsoid, completely covering the placenta, where known. The fruit, as the ovary, is fully erect, and isolobous (the two valves are equal). The fruit is carried further out of the spathellum remains by the extension of the pedicel post-anthesis. The two valves dehisce but usually persist in the fruit. The seeds are mucilaginous where known as usual in the family. <b>DISTRIBUTION</b>. Tropical West Africa: Guinea, Nigeria, Cameroon, Gabon and Angola. Eight species. <i>Sapicolella</i> species are restricted to Africa and extend from the Guinea Highlands of Guinea-Conakry in west Africa (newly recorded here) to Angola (newly reported here) in western southcentral Africa. They are not recorded from the Congo basin, nor eastern Africa. The geographic range of the genera <i>Talbotiella</i> Baker f., (Leguminosae, nine species of evergreen tree) recently also extended to Guinea (van der Burgt <i>et al.</i> 2018), is similar to that of <i>Sapicolella</i> although that genus does not extend to Angola (Mackinder <i>et al.</i> 2010). <i>Mischogyne</i> Exell (Annonaceae trees, five species, Gosline <i>et al.</i> 2019) also has a similar distribution but has an outlying species in Tanzania and one in DRC. The highest species diversity of <i>Sapicolella</i> is the Cross-Sanaga River interval of eastern Nigeria-western Cameroon which has three of the eight species: <i>S. marginalis, S. flabellata,</i> and <i>S. ijim.</i> The Cross-Sanaga River interval area contains the highest species and generic diversity of flowering plants per degree square in Tropical Africa according to several studies (Barthlott <i>et al.</i> 1996; Dagallier <i>et al.</i> 2020) possibly in part because it corresponds with the Cameroon Highlands (Cheek <i>et al.</i> 2001). Many of the species and some genera (e.g. <i>Medusandra</i> Brenan (Peridiscaceae, Breteler <i>et al.</i> 2015; Soltis <i>et al.</i> 2007) are both endemic and threatened. <i>Sapicolella</i> species are known only from the five countries mentioned but are likely to be found in intervening areas such as Sierra Leone, Liberia, Ivory Coast and Congo- Brazzaville. Of the eight known species, four are point endemics. <b>HABITAT</b>. <i>Sapicolella</i> only grows, as with most Podostemaceae, in sites with seasonally or permanently, fast-flowing, well aerated, silt-free fresh water. They are always associated with waterfalls and rapids. Unusually among African Podostemaceae genera, about half the known species of <i>Sapicolella</i> occur mainly in the 700 – 1300 m altitudinal range, when other genera are predominantly restricted to lowland elevations. However, <i>S. nana, S. flabellata, S. deniseae</i> and <i>S.</i> sp. Aall occur in the (100 –) 300 – 700 m altitudinal band. The species of the genus appear to avoid coastal areas. Although Cameroon has the highest species diversity of both <i>Sapicolella</i> and Podostemaceae in Africa, <i>Sapicolella</i> is absent from the most species-diverse Podostemaceae site (which has 10 species) the Lobé Falls near Kribi, at the coast in the lowland evergreen forest belt (Cheek <i>et al.</i> 2017b). However, all but one of the eight species of <i>Sapicolella</i> co-occur at least once with one or several other species of Podostemaceae (see individual species accounts). The exceptions is <i>S. ijim,</i> which is was not observed to occur with other Podostemaceae, possibly because of its unusual ecological niche. <i>Sapicolella ijim</i> is unique in the genus in that it flowers in the sprayzone of a waterfall, and it is not immersed in water immediately before flowering as is usual in other species. However, <i>Ledermanniella prasina</i> J.J.Schenck &amp; D.W.Thomas of the Korup has the same ecology (Schenk &amp; Thomas 2003) and <i>L. letouzeyi</i> C.Cusset of the Bakossi Mts can also occur in the spray-zone of waterfalls although not exclusively as does <i>Sapicolella ijim</i> (Cheek <i>et al.</i> 2003). Pollination &amp; Hybridisation Although we suspect that pollination is by flying insects such as bees, as reported in other African podostemoids (Cheek <i>et al.</i> 2017b), no floral visitors have been reported or observed thus far for any <i>Sapicolella</i> species. Hybridisation, reported for the first time in African Podostemaceae in Cheek <i>et al.</i> (2017b) is not known in <i>Sapicolella.</i> Since none of the species is sympatric, this is not unexpected. Habitat partitioning In those four species of <i>Sapicolella</i> that co-occur at sites with other Podostemaceae species, it has not been possible to study habitat partitioning except for <i>Sapicolella futa</i> at one site in Guinea: Case study: Salaa Falls, Futa Djalon, Guinea-Conakry At this site four species of Podostemaceae occur in close proximity some tens of metres downstream from the main tourist falls. At one point, all four can be found within a 1 m by 1 m square. When observed by MC and DM in Jan. 2018, midway through the dry season, <i>Stonesia heterospathella</i> G.Taylor was in fullflower, having been exposed by the slowly falling water in recent weeks, while <i>Ledermanniella guineense</i> C.Cusset, growing deeper in the water than any other species, was just beginning to flower. Highest up the gradually sloping flat rock surfaces were colonies of <i>Tristicha trifaria</i> Spreng., long dead. <i>Sapicolella futa</i>, also long dead, grew on the rock surface 20 – 100 cm above the level of the water surface, in a band below the <i>Tristicha</i> and above the <i>Stonesia</i>, plants of the two species intermingling at the interfaces. This same zonation, with <i>Tristicha</i> (above) and <i>Stonesia</i> (below) the <i>Sapicolella futa</i> was also seen just above the main Kambadga Falls near Pita, where <i>Sapicolella futa</i> was much rarer. <i>Sapicolella futa</i> appears to grow or compete better in slightly deeper water, than the <i>Tristicha</i>, and needs a shorter growing season (a shorter period underwater) than both the <i>Stonesia</i> and <i>Ledermanniella</i>. Conservation status The principal threats to <i>Sapicolella</i> species apply to Podostemoideae species as a whole, especially in Africa. Because they are restricted to habitats with clean, non-turbid, aerated water, with a rock substrate, degradation of any these environmental factors pose threats. Given that so many Podostemaceae species, including <i>Sapicolella</i>, are restricted to only one or two locations, they are especially at risk. Athreat at even one location is likely to pose a high extinction risk for any <i>Sapicolella</i> present. All of the species are provisionally assessed as either Endangered or Critically Endangered using the IUCN 2012 standard. Turbidity &amp; eutrophication threats Turbidity in the water, indicating that silt is present, can reduce establishment of seedlings (Philbrick &amp; Novelo 1995). It can also reduce photosynthesis during the main growth period, when plants are under water in the wet season (Cheek <i>et a</i>
description: Published as part of <i>Cheek, Martin, Molmou, Denise, Magassouba, Sekou &amp; Ghogue, Jean-Paul, 2022, Taxonomic revision of Saxicolella (Podostemaceae), African waterfall plants highly threatened by Hydro-Electric projects, pp. 403-433 in Kew Bulletin 77 (2)</i> on pages 405-410, DOI: 10.1007/s12225-022-10019-2, http://zenodo.org/record/7599361
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