| Abstract Detail
Anatomy and Morphology Gama, Gugu [1], Oskolski, Alexei [2]. Comparative stem anatomy of South African species of Grewia and related genera (Malvaceae). Grewia L. is a genus of Malvaceae comprising about 300 species distributed in Africa, Asia and Australia, with 27 species in South Africa. The current study focused on anatomy of juvenile and mature stems of eleven South African species of Grewia with inclusion of Microcos paniciulata L. and Corchorus kirkii N.E.Br. (related genera of Malvaceae). The aim was to clarify the anatomical background of the wing formation, diversity and evolution within Grewia and related taxa. In addition, phylogenetic analysis was performed with an additional of 16 more African Grewia species using Maximum Parsimony (MP) and Bayesian Inference (BI) and the plastid regions (rbcLa and matK). This analysis confirmed monophyly of the core clade of Grewia and (with lesser support) for three subclades corresponding the sections Pluriovalatae, Axillares and Microcos of Burret’s (1910) classification. All species studied shared presence of mucilage cavities in secondary phloem and cortex, stratified and conspicuous radial dilation of secondary phloem, simple perforation plates, alternate intervessel pits and the occurrence of tile cells in secondary xylem rays. G. microthrysa L., Microcos paniculata and Corchorus kirkii were distinct from other species by the absence of mucilage cavities in cortex and secondary phloem. Thus, the presence of mucilage cavities in secondary phloem is synapomorphic for Grewia, whereas the occurrence of these structures in cortex was gained in the subclade comprising G. lasiocarpa E. Mey.ex Harv., G. robusta Burch. and G. occidentalis L., and, independently, in G. villosa Willd. Both molecular and anatomical evidence confirmed the generic rank of Microcos and the placement of G. microthyrsa and G. transzambesica to this genus. Two evolutionary shifts from scanty paratracheal or vasicentric axial parenchyma to apotracheal one was observed. Such an extraordinary variation of this (usually very conservative) trait within the same genus further allows for a broader survey. The lobed stem with prominent wing portions of secondary phloem of G. caffra and probably also G. flavescens showed irregular activity of single cambium with alternation of the zones of normal bifacial cambial activity and the zones of its dormancy. This condition (also reported in some Fabaceae and Urticaceae) is considered as a new type of cambial variants. This is the first report of cambial variant for the plant order Malvales based on anatomical evidence. The loss of rhytidome in G. caffra and G. flavescens thought to be associated with the persistence of mucilage cavities enabling more effective water supply during dry season.
1 - University of Johannesburg, Department of Botany and Plant Biotechnology, Department of Botany and Plant Biotechnology, University of Johannesburg, P.O. Box 524, Auckland Park 2006, Johannesburg, South Africa, 3879 Atlas street Lenasia South ext 4 1829, Johannesburg, Gauteng, 2095, South Africa
2 - University of Johannesburg, Department of Botany and Plant Biotechnology, Department of Botany and Plant Biotechnology, University of Johannesburg, P.O. Box 524, Auckland Park 2006, Johannesburg, South Africa, Botanical Museum, Komarov Botanical Institute of t, Johannesburg, Gauteng, 2095, South Africa
Keywords:
Grewioideae
Lianas
wood anatomy
secondary phloem
development
evolution.
Presentation Type: Oral Paper
Session: AM1, Anatomy and Morphology
Location: Virtual/Virtual
Date: Wednesday, July 29th, 2020
Time: 12:45 PM
Number: AM1011
Abstract ID:480
Candidate for Awards:None |
