Molecular phylogeny, taxonomy and distribution of Chlorophytum Ker-Gawl. (Asparagaceae) in Uganda

Abstract

The study aimed to establish the phylogeny, review the taxonomic circumscription and establish the current distribution of Chlorophytum species in Uganda. Seventy districts were surveyed between June 2019 and January 2020. One hundred and forty voucher specimens were collected following standard herbarium procedures. Leaf samples for DNA studies were picked from the vouchers and dried in ziplock silica gel-containing bags. Fifteen taxa constituting 13 species were determined based on morphological characters. Total genomic DNA was extracted from silica-dried leaf samples using the E.Z.N.A.® SP Plant Mini Kit. One nuclear (ITS), and 5 chloroplast regions (trnL-F spacer, trnL intron, rps16 intron, rpl20- 5’rps12 and psbA-trnH) were PCR-amplified and sequenced. Additional sequences from different regions of Africa were added from GenBank. Phylogenetic analyses followed Bayesian and Parsimony approaches. Analysis of morphometric data generated a UPGMA phenogram based on the Gower and Jaccard coefficients. Scanning Electron Microscopy of seed surfaces that included nine species from Uganda was for the first time carried out. A distribution map was generated from herbarium records and field coordinates. Non-Metric Multidimensional Scaling of the habitat data was done to determine the habitat preferences for Chlorophytum species in Uganda. The ITS and cpDNA phylograms revealed that with the exception of C. hirsutum and C. tuberosum, all the accessions from Uganda fit into the known informal clades of Chlorophytum albeit with marked genetic distinctness from similar species of other African floras. Seed micrographs and morphometric studies revealed variations within the accessions of C. blepharophyllum and C. tuberosum. The U1 floral region had the highest number of species (11). Both U2 and U4 had four species each, whereas no record was made in the U3. Chlorophytum tordense, C. elgonense and C. blepharophyllum were the most common species while C. longifolium, C. filipendulum and C. gallabatense were the least common in this study. Chlorophytum longifolium is a new record for Uganda. The study revealed that species of Chlorophytum were more common in undisturbed habitats of open woodland and wooded grassland, while nitisols influenced the occurrence of most Chlorophytum species. Chlorophytum elgonense was reinstated at species level; and C. tuberosum may have to be referred to the genus Anthericum. The study also provides a revised key of the species of Chlorophytum that occur in Uganda. Further phylogenetic analyses representing a wider geographic and taxonomic sampling, and also extended field conservation assessments are recommended.