Taxonomy, ecology and conservation of selected rare and threatened Kniphofia species

Abstract

Kniphofia is a genus of 71 species with an African distribution. Forty-eight of these occur in southern Africa. The genus has several taxonomic issues that require investigation, and these difficulties are related to intermediate forms that put these species' taxonomic status in doubt. There are currently 14 threatened species of Kniphofia as reported on the SANBI Redlist, however, a detailed study on the threats and population size structure has only been conducted on one Critically Endangered (CR) species, Kniphofia umbrina from Eswatini. This study was prompted by a lack of knowledge concerning the current population sizes, structures, threats, and distribution of 13 other threatened taxa. Most of these 13 taxa are poorly known taxonomically. The aim was to revise the taxonomic status of five threatened Kniphofia taxa (K. leucocephala, K. pauciflora, K. drepanophylla, K. ichopensis var. aciformis, and K. crassifolia), and their five morphologically similar congeneric species (K. baurii, K. ichopensis var. ichopensis, K. laxiflora, K. angustifolia, and K. fibrosa) (eight species plus two varieties), conduct population studies on these species, and assess their conservation status. Morphological characters (qualitative and quantitative) were evaluated in 191 specimens from South African herbaria. The data were analysed using the Statistical Package for the Social Sciences (SPSS) and Paleontological Statistics (PAST). The findings relating to K. leucocephala and K. pauciflora suggest that the two species are morphologically similar, although they exhibit different flower colours. The two species show a different altitudinal range, differ in flowering time and are distributed in different vegetation types. Morphological and flowering similarities were also noted between K. baurii and K. drepanophylla. These two species differed in altitude and vegetation type. A close morphological similarity between K. baurii and K. fibrosa was noted but needs further investigation. Kniphofia ichopensis var. ichopensis was morphologically similar to K. ichopensis var. aciformis and K. angustifolia but significantly different to K. laxiflora. Similar flowering times were noted between K. ichopensis var. ichopensis and K. ichopensis var.aciformis, while those of K. angustifolia and K. laxiflora differed. There was no altitudinal difference between K. ichopensis var. ichopensis and both K. ichopensis var. aciformis and K. laxiflora. However, K. angustifolia differed in altitude from K. ichopensis var. ichopensis. Their distribution within vegetation types also differed among all these species. Due to the absence of herbarium material for K. crassifolia, the study could not establish its taxonomic relationship with K. fibrosa. A neotype was designated for K. leucocephala in this study due to a missing type specimen. Although the study recognised most of the compared Kniphofia species as morphologically indistinguishable species, taxonomic changes were not made due to a lack of a detailed phylogenetic study inclusive of all the species in this genus. Therefore, the status quo of the currently recognised morphological units and Codd species concept is maintained at present. The study also recognised the work done by Ramdhani et al. (2009) but suggests that the work needs to be expanded to better understand monophyly and species relationships within this genus. A single population of each of the paired Kniphofia species was assessed in KwaZulu-Natal, and the combined population sizes were found to be very low (220 individuals), of which 44% were reproductive adults. Least Concern (LC) species had higher population sizes compared to threatened species, with sizes ranging from 14 to 40 plants. Bimodal and J-shaped size class distribution (SCD) were the most common across all populations, suggesting episodic recruitment and the domination of adult individuals. Of the three measures of SCD explored, plant height was the preferred measure for these species. Most of these populations were in areas dominated by grassy vegetation, with disturbance factors such as the prevalence of invasive alien plant species (IAPs), rubbish dumping, trampling, and overgrazing, which may cause habitat degradation. Field search of K. crassifolia subpopulations was fruitless, suggesting a possible extinction in the wild. Using population data from this current study, the status of K. leucocephala and K. pauciflora was confirmed to be Critically Endangered (CR). This is due to high risks from IAP species such as Eucalyptus, urban expansion, reduction in habitat quality and low Area of Occupancy (AOO) and Extent of Occurrence (EOO). Although K. drepanophylla currently has 15 populations, only one is known to be in a conserved area, and the populations outside the nature reserves face a higher risk of trampling, uncontrolled fires, overgrazing, and harvesting on communal land. Therefore, the study proposes a Vulnerable (VU) category and immediate re-assessment of the other populations that were not surveyed during this study to confirm this proposed status. There was limited information on the status of K. ichopensis var. aciformis prior to this study; however, it has been established that there are only four currently known populations of this species. The surveyed population is threatened by cattle trampling, overgrazing and unmanaged IAP, and three of its populations occur in habitats that are poorly protected, which also makes it vulnerable to extinction. Therefore, a VU category is proposed for this species. Although K. baurii, K. ichopensis var. ichopensis, K. laxiflora, K. angustifolia, and K. fibrosa are listed as LC, there were few individuals (all <40) in each of these populations. These populations were mainly threatened by trampling from humans and livestock, harvesting, rubbish dumping, IAP and overgrazing. The results suggest that although these species are categorised as LC, they are facing a serious decline due to multiple threats and will also need conservation and monitoring directed towards them. The current conservation status for these species was provisionally retained, but more extensive surveys, preferably of all known populations, are a priority. The study provided baseline information for suitable conservation adaptive management plans, with fencing populations outside conserved areas proposed. Further studies are needed to assess suitable fire regimes and the potential to augment them with additional seedlings to increase their viability, given the very small population sizes.