Histological and cytological analysis of microsporogenesis and microgametogenesis of the invasive species Galinsoga quadriradiata Ruiz & Pav. (Asteraceae)

Galinsoga quadriradiataRuiz & Pav. is an annual weedy plant that can be found all over the world. It belongsto the Asteraceae family and is recognised as one of the invasive foreign plants in Poland, which are native toCentral and South America. The aim of this study was to describe the reproductive features of Galinsoga quadri-radiatafocusing on the changes that occur during microsporogenesis and microgametogenesis along with themorphology of its pollen. As it is typical of the eudicot clade of Angiosperms, cytokinesis of G. quadriradiataissimultaneous. The pollen grains are tricolporate with spiny outer walls and the course of the microsporogenet-ic process is fairly typical of the Echinatae group of weed plants. The high viability of the pollen grains, whichmature unequally in the inflorescences, and the proper course of meiosis determine whether a plant has theinvasive character of Galinsoga quadriradiata

Comparative anatomy of ovules in Galinsoga, Solidago and Ratibida (Asteraceae)

Many Asteraceae species have been introduced into horticulture as ornamental or interesting exotic plants. Some of them, including Solidago and Galinsoga, are now aggressive weeds; others such as Ratibida are not. Special modifications of the ovule tissue and the occurrence of nutritive tissue have been described in several Asteraceae species, including invasive Taraxacum species. This study examined whether such modifications might also occur in other genera. We found that the three genera examined – Galinsoga (G. quadriradiata), Solidago (S. canadensis, S. rigida, S. gigantea) and Ratibida (R. pinnata) – differed in their nutritive tissue structure. According to changes in the integument, we identified three types of ovules in Asteraceae: “Taraxacum” type (recorded in Taraxacum, Bellis, Solidago, Chondrilla), with well-developed nutritive tissue having very swollen cell walls of spongy structure; “Galinsoga” type (in Galinsoga), in which the nutritive tissue cells have more cytoplasm and thicker cell walls than the other integument parenchyma cells, and in which the most prominent character of the nutritive tissue cells is well-developed rough ER; and “Ratibida” type (in Ratibida), in which the nutritive tissue is only slightly developed and consists of large highly vacuolated cells. Our study and future investigations of ovule structure may be useful in phylogenetic analyses

Ovule structure of Scotch thistle Onopordum acanthium L. (Cynareae, Asteraceae)

Studies concerning the ultrastructure of the periendothelial zone integumentary cells of Asteraceae species arescarce. The aim was to check whether and/or what kinds of integument modifications occur in Onopordum acanthium. Ovule structure was investigated using light microscopy, scanning electron microscopy, transmission electron microscopy and histochemistry. For visualization of calcium oxalate crystals, the polarizing microscopy was used. The periendothelial zone of integument in O. acanthium is well developed and composed of mucilage cells near the integumentary tapetum and large, highly vacuolated cells at the chalaza and therefore they differ from other integumentary cells. The cells of this zone lack starch and protein bodies. Periendothelial zone cells do not have calcium oxalate crystals, in contrast to other integument cells. The disintegration of periendothelial zone cells was observed in a mature ovule. The general ovule structure of O. acanthium is similar to other members of the subfamily Carduoideae, although it is different to “Taraxacum”, “Galinsoga” and “Ratibida” ovule types

Reduced pollen viability and achene development in Solidago ×niederederi Khek from Poland

Pollen and achene characters of natural interspecific hybrid Solidago ×niederederi Khek were analyzed and compared with putative parental species S. virgaurea L. and S. canadensis L. to estimate the level of disturbances in generative reproduction resulting from its hybrid nature. Pollen viability (stainability) of Solidago ×niederederi from one newly discovered locality in NE Poland was evidently reduced to ~65% in both viability tests (acetocarmine and Alexander). The diameter of viable pollen (median 21.11 µm) fell between S. canadensis (median 19.52 µm) and S. virgaurea (median 23.48 µm). Both parental species produced normally developed achenes with high frequency (~90%) whereas in the hybrid, the seed set was dramatically low (6%). The results clearly indicated that sexual reproduction of hybridogenous taxon S. ×niederederi is disturbed, and its potential impact as an invasive species depends mainly on vegetative propagation