Seedling structure in Asteraceae weedy species: considerations on the vasculature system. The vasculature system of the seedling is of interest since it represents the first mature vascular coordination between shoot and root, which was foreshadowed in the procambial system of the embryo. In this study, seedlings of ten Asteraceae weedy species were analyzed focusing on the vasculature system using a morpho and anatomical approach. The roots were found to be diarch and tetrarch, the species have intermediate or high root/shoot transition, and the cotyledons develop an independent double leaftrace and a common simple-leaf trace. The transition region of the seedlings is strikingly different when compared with other families, such as, Annonaceae, Cactaceae, Fabaceae, Myrtaceae, Amaranthaceae, Clusiaceae, and Rutaceae. In spite of the uniformity in the vascular arrangement among the Asteraceae seedlings, the conclusion attained from this study is that some essential structural details may be of diagnostic value, such as the stele arrangement, the level of the transition zone, the cotyledon sheath, and the splitting of the phloem. Further, the presence of trilacunar node in the Asteraceae can be the result of a reversal evolutionary process (homoplasy) during the life history of the family.
Studies on seed structure of Asteraceae have received little attention of botanists. Seed structure in Asteraceae is analyzed to evaluate the usefulness of characters in the separation of species through the analysis of nine weedy species. Seeds originate from anatropous, unitegmic and tenuinucellate ovules. The partial collapse of the developing seed coat is a common characteristic in the Asteraceae species studied. The testa consists of crushed and thin-walled cells in almost all of the species studied herein, except for Elephantopus mollis and Parthenium hysterophorus, which showed exotesta cells with U-shaped thickening. The analysis revealed high uniformity in seed characters.
Chamaesyce prostrata (Aiton) Small, Euphorbia heterophylla L. and Euphorbia graminea Jacq. are weedy species that occur with relative frequency in the region of Maringá, Paraná State, Brazil. Data about the morphology and anatomy of seedlings of these species were obtained, with emphasis on significant structural differences of seedlings between species of Euphorbia and Chamaesyce. Seedlings are phanerocotylar and epigeal. Root is axial and triarch. Cotyledons are leaf-like and dorsiventral. Eophylls and prophylls are simple and dorsiventral. Morphological variations occur in the cotyledon shape of Euphorbia seedlings. It is remarkable the Kranz structure of leaves that occurs only in Chamaesyce.Estrutura da plântula de espécies de Euphorbia L. e Chamaesyce Gray RESUMO. Chamaesyce prostrata (Aiton) Small, Euphorbia heterophylla L. e E. graminea Jacq. (Euphorbiaceae) são espécies invasoras frequentes na região de Maringá, Paraná. Foram obtidos dados sobre a morfologia e anatomia das plântulas dessas espécies, com ênfase se há caracteres estruturais significativos das plântulas entre as espécies de Euphorbia e Chamaesyce. As plântulas são fanerocotiledonares e epígeas. A raiz é axial e triarca. Os cotilédones são foliáceos e dorsiventrais. Os eofilos e profilos são folhas simples e dorsiventrais. As variações mofológicas ocorrem no formato dos cotilédones das plântulas de Euphorbia. Sob o aspecto anatômico é especialmente notável a estrutura Kranz das folhas que ocorrem somente em Chamaesyce.Palavras-chave: plantas invasoras, raiz, hipocótilo, cotilédones, epicótilo, eofilos.
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