Embryological studies in Taraxacum udum Jordan (sect. Palustria)

The present paper reports our observations on the mode of reproduction in Taraxacumudum (sect. Palustria), a very rare species in Poland, known only from a single locality. Based on the analysis of the developmental processes in the ovules, it can be concluded that this bog dandelion is an obligate and autonomous apomict. Its reproduction involves (i) restitutional diplospory, also known as Taraxacum type; (ii) parthenogenesis; and (iii) autonomous endosperm formation. Moreover, observations on the anatomy of ovules confirmed the occurrence of a special storage tissue around the embryo sac, which is considered to be an additional source of nutrition for the embryo. An examination of the anthers showed that, in spite of highly disturbed meiosis, apomictic T. udum produces pollen but pollen grains are heterogeneous in size and stainable using an acetocarmine test. Key words: Taraxacum, apomixis, diplospory, parthenogenesis, autonomous endosperm, microsporogenesis, pollen grains. Resume : Les auteurs presentent des observations sur le mode de reproduction du Taraxacum udum (sect. Palustria), une espece endemique de la Pologne, dont une seule localite est connue. Sur la base de l'analyse des processus de developpement dans les ovules, on peut conclure que ce pissenlit de tourbieres constitue une espece apomictique obligatoire et autonome. Sa reproduction implique (i) une diplosporie restitutionnelle, egalement connue comme de type Taraxacum,(ii) la parthenogenese, et (iii)la formation autonome de l'endosperme. De plus, des observations de l'anatomie des ovules confirment la presence de tissus speciaux d'emmagasinage autour du sac embryonnaire, consideres comme source additionnelle de nutriments pour l'embryon. L'examen des antheres montre que, en depit d'une meiose fortement perturbee, le T. udum apomictique produit du pollen, mais les grains de pollen sont de dimensions heterogenes et colorables a l'acetocarmin. [Traduit par la Redaction] Mots-cles: Taraxacum, apomixie, diplosporie, parthenogenese, endosperme autonome, microsporogenese, grains de pollen.
Introduction Members of the genus Taraxacum Wigg. (Asteraceae-Cichorioideae) are some of the most common plants spread throughout the temperate zone of both the northern and southern hemisphere. The western Himalayan [...]