Um Novo e Peculiar Tipo de Sistema Subterrâneo em Espécies de Vernonia da Serra do Cipó (Minas Gerais, Brasil)

Get the shovel: morphological and evolutionary complexities of belowground organs in geophytes

Herbaceous plants collectively known as geophytes, which regrow from belowground buds, are distributed around the globe and throughout the land plant tree of life. The geophytic habit is an evolutionarily and ecologically important growth form in plants, permitting novel life history strategies, enabling the occupation of more seasonal climates, mediating interactions between plants and their water and nutrient resources, and influencing macroevolutionary patterns by enabling differential diversification and adaptation. These taxa are excellent study systems for understanding how convergence on a similar growth habit (i.e., geophytism) can occur via different morphological and developmental mechanisms. Despite the importance of belowground organs for characterizing whole-plant morphological diversity, the morphology and evolution of these organs have been vastly understudied with most research focusing on only a few crop systems. Here, we clarify the terminology commonly used (and sometimes misused) to describe geophytes and their underground organs and highlight key evolutionary patterns of the belowground morphology of geophytic plants. Additionally, we advocate for increasing resources for geophyte research and implementing standardized ontological definitions of geophytic organs to improve our understanding of the factors controlling, promoting, and maintaining geophyte diversity.

Morpho-anatomy and ontogeny of the underground system of Chrysolaena simplex (Less.) Dematt. (Asteraceae)

The occurrence of thickened underground systems in Asteraceae is widely reported in the literature. Given the great complexity of underground systems, which may originate from roots, stems, or both, morpho-anatomical analyses are essential to ensure the use of correct terminology. The goals of this study were to describe the morpho-anatomy and ontogeny, investigate the occurrence of secondary metabolites and evaluate the effects of seasonality on the underground system of Chrysolaena simplex (Less.) Dematt. Samples were studied using standard protocols of plant anatomy, scanning electron microscopy, histochemical and phytochemical. The underground system of C. simplex was categorised as a rhizophore which started from cotyledonary node. In adult individuals, with rhizophores completely developed, the primary roots degenerated and adventitious radicular systems are formed. The buds in the subterranean portions promote the rhizophore growing, and form aerial stems when exposed to light. Lipophilic droplets were evident in the parenchymatous cells of the cortex and pith, endodermis and buds. Inulin-type fructans were observed in the stem axis and buds of the rhizophore. The presence of buds, secondary metabolites and the storage of fructans and lipids in the rhizophore can be seen as adaptive traits.

Morfoanatomia do sistema subterrâneo de Smilax subsessiliflora (Smilacaceae)

Resumo Smilax subsessiliflora Duhamel, espécie exclusivamente brasileira, tem por habitat a floresta Atlântica, mesófila e as matas de restinga. Este trabalho tem por objetivo descrever a morfoanatomia do sistema subterrâneo de S. subsessiliflora. O sistema subterrâneo da espécie em questão é constituído pelo rizóforo, do qual partem os ramos caulinares e as raízes adventícias. O rizóforo apresenta epiderme uniestratificada com estômatos, córtex com células de paredes espessadas e lignificadas, meristema de espessamento primário e cilindro vascular, integrado por feixes colaterais. Das raízes adventícias que partem do rizóforo originam-se outras que se distinguem pelo calibre e pela cor. Aquelas apresentam córtex externo, constituído por células parenquimáticas e córtex interno, constituído por esclereídes, que passam a exercer a função de revestimento, após a eliminação do córtex externo. O cilindro vascular é poliarco e sifonostélico. Grãos de amido ocorrem no periciclo e na medula. No córtex das raízes laterais detectaram-se endomicorrizas arbusculares. As características anatômicas observadas no sistema subterrâneo de S. subsessiliflora se assemelham às relatadas para o rizóforo de S. quinquenervia.