Abstract
The structure of Agapanthus africanus and A. praecox flowers was studied on permanent cross-sectional and longitudinal sections using a light microscope. The genus Agapanthus belongs to the subfamily Agapanthoideae, the family Amaryllidaceae, which is characterized by the presence of the upper ovary, septal nectaries and fruit – fleshy capsule. Micromorphological studies of the flower are considered as a way for detection of unknown plant features, adjustment of plants to specialized ways of pollination and determining the first stages of morphogenesis of fruit, and further use these features in taxonomy. 10 flowers of A. africanus and A. praecox were sectioned using standard methods of Paraplast embedding and serial sectioning at 20 micron thickness. Sections were stained with Safranin and Astra Blau and mounted in Eukitt. It was found that in the studied species the tepals have single-bundle traces. The vascular system of the superior ovary consists of a three bundle dorsal vein, of the ventral roots complex, which are reorganized into paired ventral bundles of the carpel, which form traces to ovules. For the first time, the following gynoecium zones were detected in A. africanus: a synascidiate structural zone with a height of about 560 μm and a fertile symplicate structural zone with a height of about 380 μm and a hemisymplicate zone of 2580 μm. In A. praecox gynoecium, there is a synascidiate structural zone with a height of 200 μm and a symplicate structural zone of 600 μm and a hemisymplicate zone of 620 μm. Septal nectaries appear in the hemisymplicate zone and open with nectar fissures at the base of the column, with a total septal nectar height of 2880 μm in A. africanus and 820 μm in A. praecox. The ovary roof is 300 µm in A. africanus and 200 µm in A. praecox. Triple dorsal bundles of carpels in A. africanus have been identified, which could be considered as adaptation of different stages of morphogenesis of fruit to dehiscence. The new data obtained by the vascular anatomy of the flower and the presence of different ovary zones significantly add to the information about anatomical and morphological features of the studied species, which can be further used in the taxonomy of the family Amaryllidaceae.
Highlights
Molecular-phylogenetic analysis allows the division of genera, subfamilies and families, by molecular characteristics, but scientists do not always take into account such important features of flower structure as features of vascular anatomy and structure of septal nectaries, the presence and height of ovarian zones, the basis for taxonomic systems may be signs of flower micromorphology
The study of micromorphology and vascular anatomy of monocotyledonous flowers and fruits is a modern direction in the study of evolutionary morphology (Odintsova & Fishchuk, 2017; Skrypec & Odintsova, 2020)
New features of the anatomical structure of the flower A. africanus and A. praecox, which we found, are the presence of three-bundle dorsal carpel bundles in A. africanus and single-bundle in A. praecox, the presence of a ventral complex that is reorganized into paired ventral vascular bundle, the presence of a high ovary base and the ovary roof, the presence of synascidiate, symplicate and a hemisymplicate gynoecium structural zones
Summary
Molecular-phylogenetic analysis allows the division of genera, subfamilies and families, by molecular characteristics, but scientists do not always take into account such important features of flower structure as features of vascular anatomy and structure of septal nectaries, the presence and height of ovarian zones, the basis for taxonomic systems may be signs of flower micromorphology. The objects of our study were Agapanthus africanus (L.) Hoffmanns and A. praecox Willd. They belong to the genus Agapanthus, subfamily Agapanthoideae, family Amaryllidaceae (Chase et al, 2009; Chase et al, 2016). Yeo placed Agapanthus in the family Alliaceae, closer to the genus Tulbaghia (Dahlgren et al, 1985). In 1996, after phylogenetic analysis of the DNA sequences of the rbcL gene, Themidaceae was returned and Agapanthus was removed from Alliaceae (Fay & Chase, 1996). The authors found that Agapanthus is a sister clade to the subfamily Amaryllidaceae and moved it to this family. The family Agapanthaceae included only the genus Agapanthus
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