Electronic identification keys for species with cryptic morphological characters: a feasibility study using some Thesium species

Abstract

The popularity of electronic identification keys for species identification has increased with the rapid technological advancements of the 21st century. Although electronic identification keys have several advantages over conventional textual identification keys and work well for charismatic species with large and clear morphological characters, they appear to be less feasible and less effective for species with cryptic morphology (i.e. small, obscure, variable characters and/or complicated structures associated with terminology that is difficult to interpret). This is largely due to the difficulty in presenting and illustrating cryptic morphological characters unambiguously. When taking into account that enigmatic species with cryptic morphology are often taxonomically problematic and therefore likely exacerbate the taxonomic impediment, it is clear that species groups with cryptic morphology (and all the disciplines dependent on their correct identification) could greatly benefit from a user-friendly identification tool, which clearly illustrates cryptic characters. To this end, the aim of this study was to investigate and develop best practices for the unambiguous presentation of cryptic morphological characters using a pilot interactive photographic identification key for the taxonomically difficult plant genus Thesium (Santalaceae), as well as to determine its feasibility. The project consisted of three stages: (1) software platform selection, (2) key construction and (3) key evaluation. The proposed identification key was produced with Xper3 software and can be accessed at http://www.xper3.fr/xper3GeneratedFiles/publish/identification/1330098581747548637/mkey.html. Methodologies relating to amongst others, character selection and delineation, visual and textual descriptions, key construction, character coding and key evaluation are discussed in detail. Seventeen best practices identified during this study are subsequently suggested for future electronic key compilation of species with cryptic morphology. This study indicates that electronic identification keys can be feasible and effective aids for the identification of species with cryptic morphological characters when the suggested best practices are followed.

Thesium hispidifructum (Santalaceae), a New Hispidulous Species from Limpopo, South Africa and Notes on Enigmatic T. celatum

“…A thorough study of all known diagnostically important morphological characters in Thesium, as defined and used in prior studies [3,[6][7][8][11][12][13][14][15]17,18], revealed that six vegetative and 12 reproductive characters (Table 1) are useful when distinguishing among the unknown Thesium species and five morphologically similar species (T. burchellii A.W.Hill, T. gracilarioides A.W.Hill, T. megalocarpum A.W.Hill, T. procerum N.E.Br., and T. whyteanum Rendle). These characters are: (1) maximum plant height, (2) growth form, (3) habit, (4) branching pattern, (5) indumentum, (6) leaf length, (7) inflorescence type, (8) number of flowers per inflorescence, (9) bract length, (10) presence or absence of involucral bracts, (11) pedicel/peduncle length, (12) flower length, (13) hypanthium length, (14) flower lobe length, (15) style length, (16) stamen placement, (17) placental column shape, and (18) fruit stipe length.…”

“…Knowledge was generated through multiple collections made of a relatively poorly known Thesium species in the Waterberg. It was described by Brown in 1932 [18] using a cryptic diagnosis and was represented by limited material in herbaria. Through collections made over the past few months and photos taken of critical characters and uploaded onto iNaturalist, puzzle pieces were fit together to determine the identity of T. celatum and establish a better-informed, comprehensive morphological description.…”

“…Although neither T. celatum nor T. hispidifructum have been included in molecular phylogenies of the genus (e.g., [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]), they both likely form part of subgenus Psilothesium (A.DC.) Zhigila, Verboom, and Muasya.…”

“…Measurements were taken either by hand using a ruler or those less than 3 mm using an Olympus DSX110 digital microscope with Olympus DSX software v. 3.1.9 (Olympus Corporation 2011-2019, Tokyo, Japan). All morphological characters known to be of diagnostic value (habit, growth form, plant indumentum, leaf morphology, inflorescence structure and flower morphology and indumentum), following previous studies (e.g., [6][7][8]12,13,17,18]) and expert knowledge, were studied and noted. Second, an attempt was made to key out the unknown species using two available identification keys and the measurements that were taken in step one [6,7].…”

The five key types of Marsilea crenata as a potential identification tool for biology students

“…According to a previous study, the accuracy of the plant species identified, and the time required for identification are parameters of key application efficiency (Stagg et al, 2014;Stagg & Donkin, 2013). In contrast, Lombard et al (2021), stated that identification accuracy should be given more priority than time. This is because accurate organism identification is an important aspect when measuring the biodiversity of an area.…”