Abstract
The investigations involved four species of the <i>Cotoneaster</i> genus: <i>C. divaricatus</i>, <i>C. horizontalis</i>, <i>C. lucidus</i>, <i>C. praecox</i>, which are commonly grown for decorative purposes. In Poland, these plants bloom in May and June and are a source of abundant spring nectar flow for insects. The floral nectaries of the above-mentioned species were examined using stereoscopic, light, and scanning electron microscopy in order to assess their size and epidermal microstructure. In the plants studied, the upper part of the hypanthium is lined by nectariferous tissue. The nectaries in the four species vary in terms of their sizes. Nectar is secreted onto the surface of the epidermis through anomocytic, slightly elongated or circular stomata. The largest stomata on the nectary epidermis were found in the flowers of <i>C. horizontalis</i>, and the smallest ones in <i>C. divaricatus</i>.Their size and location in relation to other epidermal cells were taxon-specific. The highest density of stomata in the nectary epidermis was found in <i>C. divaricatus</i> (205 per mm<sup>2</sup>), whereas <i>C. horizontalis</i> flowers exhibited the lowest (98 per mm<sup>2</sup>) stomatal density. The cuticular ornamentation on the nectary epidermis surface was diverse. The stomatal indices calculated for the nectary epidermis were considerably lower than for the leaves in the particular species.
Highlights
The genus Cotoneaster (Rosaceae) comprises 60 species occurring in Europe, Asia and north-west Africa
In terms of the nectary size, the Cotoneaster species investigated can be arranged in the following sequence: C. lucidus > C. praecox > C. horizontalis > C. divaricatus
Previous studies (Weryszko – Chmielewska and Konarska, 1996; Weryszko - Chmielewska et al 2004) suggested the sequence: C. praecox > C. horizontalis > C. lucidus according to the decreasing thickness of nectariferous tissue
Summary
The genus Cotoneaster (Rosaceae) comprises 60 species occurring in Europe, Asia and north-west Africa. Various plant habits – from creeping shrubs to small trees – are found within the genus. The plants produce small, white or pink inflorescences that can be single or form small cymes or corymbs (Szweykowscy , 2003). The four species of the genus Cotoneaster investigated in this study are commonly planted for decorative purposes in Poland. Vilm ex Bois at Berthault originate from China. On their short shoots, they produce single or clustered (2-3) flowers with a pink or white corolla. Owing to its shoot habit, C. horizontalis is often grown in rock gardens. Its flowers characterised by white-pink corolla petals form clusters of 3-8 (15). In the Polish conditions, the species in question bloom in May and June (Szweykowscy , 2003; Seneta and Dolatowski , 2004)
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