Chlorophytum delicatulum (Asparagaceae), a newly described species from Zambia

Chlorophytum delicatulum Osborne, Vollesen & Bjorå from Zambia is described, illustrated and placed within the context of recent taxonomic and phylogenetic work on Chlorophytum in Africa. This delicate herb has leaf bases furnished with conspicuous dark red setae resembling eyelashes. Its phylogenetic position, ecology, phytogeography and conservation status are discussed. Chlorophytum delicatulum is assessed as being of Least Concern using the categories and criteria of the IUCN Red List.


Introduction
Chlorophytum Ker Gawl. (Asparagaceae: Agavoideae Anthericeae) is a genus of approximately 150 species found across the Old World Tropics (Stevens 2001). The genus is particularly diverse in eastern and southern central Africa, with 52 species occurring in the Flora of Tropical East Africa (FTEA) area (Nordal et al. 1997), 57 species in the Flora Zambesiaca (FZ) area (Kativu et al. 2008) and 52 species in the Flore d'Afrique Centrale (FAC) area (Meerts 2015). Molecular analyses of the species of Chlorophytum have shown that they can be divided into subgroups that correlate with morphological characters and number of chromosomes (Bjorå 2008;Bjorå et al. 2017).
Material of the species described here was first collected at Mutinondo Wilderness Area in Eastern Zambia in 2010, and subsequent collections were made in 2015, 2016 and 2019. An earlier collection from 1955 from Serenje, also in the same general part of Zambia, has been referred to the same taxon. When detailed studies were carried out at Kew, this material could not be matched with any known species. It is described here as Chlorophytum delicatulum Osborne, Vollesen & Bjorå.

Morphological studies
Specimens were collected and studied by S. Bidgood, L. Merrett, J. Osborne and K. Vollesen at Mutinondo and extensively photographed by L. Merrett. Live specimens were studied in situ at Mutinondo. Herbarium specimens were studied at Royal Botanic Gardens, Kew (K). SEM photographs of seeds from Bidgood et al. 8600 (K) were prepared by Aurelie Grall at Kew.

Conservation status
In order to assess the conservation status of this new species, georeferences were taken or estimated from each herbarium collection, and extent of occurrence was calculated from a minimum convex polygon using the online GeoCAT tool (Bachman et al. 2011). A provisional assessment of conservation status was obtained by applying the categories and criteria of the IUCN Red List (IUCN 2012).
RECOGNITION. Chlorophytum delicatulum is easily recognised by the combination of wiry roots with distal tubers, grass-like linear hairy leaves, racemose inflorescence, conspicuous dark red setae (resembling eyelashes) on cataphylls and basal part of the leaf margins, and bracts with long dark reddish-purple setae on veins and margins. It resembles narrow-leaved forms of C. galpinii (Baker) Kativu var. galpinii, which differ by almost always having a paniculate inflorescence, longer glabrous or very finely ciliate bracts (6 -15 mm long, 3 -6 mm long in C. delicatulum), and generally larger flowers (tepals 10 -14 mm long, 5 -9 mm long in C. delicatulum). Chlorophytum delicatulum is also similar to nar row-leaved forms o f C. rubribracteatum (De Wild.) Kativu which typically have a reddish-purple coloration on cataphylls, leaf bases, bracts and tepal apices, and paniculate inflorescences. Some forms of C. sphagnicolum Meerts from NW Zambia with racemose inflorescences resemble the new species but differ in having generally broader leaves (1 -2.5 (-3) mm wide, 0.5 -1.5 mm wide in C. delicatulum), and longer glabrous or very finely ciliate bracts ((5 -) 7 -11 mm long, 3 -6 mm long in C. delicatulum). A character matrix illustrates the   morphological differences between C. delicatulum, C. rubribracteatum, C. sphagnicolum and the varieties of C. galpinii (Table 1). These three species also differ from C. delicatulum in their ecology. Chlorophytum delicatulum grows in pockets of sandy-gravelly or sandy-peaty soils in shallow, seasonally wet depressions on large granite outcrops or in rock crevices, C. galpinii and C. rubribracteatum are typically open woodland and grassland species, while C. sphagnicolum grows in ephemeral wet or swampy grassland pans on ironstone or dolomite soils. One primary separating character for species groupings within Chlorophytum in recent floras (Nordal et al. 1997;Kativu et al. 2008;Meerts 2015) is the number of flowers per bract (either single or two to several per bract). Chlorophytum delicatulum blurs the difference between the groups insofar as the populations studied. For example, Bidgood 8231 (K) has some individuals with all flowers in an inflorescence being solitary, while others have at least some flowers paired. This variation appears not to be associated with the plants' vigour.
DISTRIBUTION. Chlorophytum delicatulum is endemic to northern-central Zambia, in Mpika and Serenje Districts (Map 1). Due to the close proximity of this area to southern DR Congo (Katanga), it is quite possible that the species will eventually also be found there. CONSERVATION STATUS. Chlorophytum delicatulum is known from only two sites in northern-central Zambia (Map 1). It has a very restricted distribution with an extent of occurrence of approximately 31 km 2 . The exact locality of the site at Serenje in Central Province, where this species was collected in 1955, is not known but is likely to be one of the hills that surround the town. There is extensive urban development and agricultural land conversion in this area, but the hills currently support natural or semi-natural vegetation and although the vegetation here is to some degree disturbed, Chlorophytum delicatulum may well still occur here. At the Mutinondo Wilderness Area in Muchinga Province, there have been five recent collections dating from 2010 -2019. The species has been observed to be fairly frequent here and does not appear to be under threat. The almost bare granitic domes where it occurs do not contain any valuable minerals or gemstones and are of no agricultural use. Few of the woody species reach a size where they are of use for firewood and charcoal production. For   When observed in the field, it is striking that plants of Chlorophytum delicatulum are never seen in groups or aggregations. Plants are always solitary, often occurring some considerable distance from the next plant. The significance of this population structure is not obvious. It could be an adaptation to herbivory (see below) or a strategy to counteract pests. This is a phenomenon also observed in several other species of Chlorophytum at Mutinondo, and here also in other plant families, e.g. in species of several genera in Apocynaceae subfam. Asclepiadoideae. ETYMOLOGY. The specific epithet refers to the slender and delicate form of the plant.

Phylogenetic position
Phylogenetic analyses were performed to place the undescribed species in relation to other species of Chlorophytum. The analyses revealed the same general pattern as reported previously (Bjorå 2008;Bjorå et al. 2017). Thus, the general structure of the phylogenetic tree will not be discussed in detail here. Both in the nuclear (ITS, Fig. 5A) and concatenated chloroplast (Fig.  5B) analyses, C. delicatulum clusters together with species that were formerly included in genus Anthericum (Baker 1898;Kativu & Nordal 1993) and now informally referred to as the "Former African Anthericum group". This group is highly supported (Fig. 5A & B, PP1/JK 100) in the molecular phylogeny and by morphology. The species are all characterised by wiry roots with distal tubers, most of them having distichous leaves, and all having shallow deltoid capsules that are transversely ridged and seeds that are irregularly folded. Species in this group are distributed from Ethiopia, southwards to the Cape, with more species occurring in southern Africa. Within this group, C. delicatulum resolves as sister to C. galpinii var.
norlindhii (Weim.) Kativu, C. rubribracteatum, C. cameronii (Baker) Kativu and C. galpinii var. matabelense (Baker) Kativu (Fig. 5A, PP 0.94/JK 74). This clade is also seen in the chloroplast tree, but without robust support (Fig.  5B). The molecular analyses do not indicate a single sister species to C. delicatulum. Rather, it resolves as distinct from the "Former African Anthericum group" sister taxa included in the analyses (Fig. 5A & B). Since only a limited number of taxa from the "Former African Anthericum group" were included in the molecular study, further research is required to unravel the relationships among the closely related C. delicatulum, C. sphagnicolum and varieties of C. galpinii.
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