Schefflera is the largest genus in the angiosperm family Araliaceae, with about 900 species, of which c. 300 belong to five subgeneric groups in the Neotropical region. Previous phylogenetic studies of Schefflera have been limited to a small number of species from this region, and very little is know about phylogenetic relationships in the Brazilian-centered Didymopanax group of this genus. Therefore, to gain a better understanding of the diversity and evolution of the Didymopanax group of Schefflera, I investigated the systematics of these plants in the broader context of the entire Neotropical clade. The main goals were (1) to investigate pollen diversity in Neotropical species of Schefflera; (2) to test the monophyly of these species; (3) to provide a taxonomic revision for species of the Didymopanax group of Schefflera; and (4) to investigate evolutionary relationships within the Didymopanax group. Pollen morphology exhibits an uneven variability across Neotropical Schefflera. For example, pollen characters support the distinctiveness of the Didymopanax group from all remaining groups. Moreover, S. tremula has a distinctive pollen morphology compared to remaining species of the Sciodaphyllum group. However, among the remaining groups of Neotropical Schefflera, pollen characters are less distinctive. Molecular phylogenetic analyses have confirmed the monophyly of the Neotropical species of Schefflera, and helped to identify four major clades. One of these clades includes subclades representing the Didymopanax and Crepinella groups, while another clade includes all species from groups Cotylanthes and Sciodaphyllum, excluding Schefflera tremula, a finding that corroborates pollen data. In the formal taxonomic revision of Didymopanax, 37 species are recognized, together with three insufficiently known species. The revision also includes updated species circumscriptions and nomenclatural adjustments for 26 names. Phylogenetic analyses among Didymopanax species recovered four morphologically and geographically coherent clades (Atlantic Forest, Imeri, Five-carpellate and Savannic clades), but their phylogenetic inter-relationships were generally weakly supported. Poorly resolved relationships in the Savannic clade suggests a rapid diversification in the campos rupestres vegetation, which accounts for the greatest species richness in the group. The presence of multiple Didymopanax lineages in the Amazonian and Atlantic forests corroborates that these regions may be composite biogeographic areas.

Orientadores: Paulo Sergio Moreira Carvalho de Oliveira, Jose Roberto Trigo / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-11T11:43:38Z (GMT). No. of bitstreams: 1 Silveira_HenriqueCesarPelicci_M.pdf: 1601394 bytes, checksum: fd0e1ab69ffeaaa903956975abcf14ec (MD5) Previous issue date: 2008 / Mestrado / Mestre em Ecologia

Die Arbeit ist in drei Teile untergliedert: Die Struktur "Hypodermales Wasserspeichergewebe" wird unter anatomischen, ökomorphologischen und evolutionsbiologischen Gesichtspunkten betrachtet. Die Anwesenheit eines farblosen Hypoderms erschwert bei der Musteranalyse variegater Periklinalchimären die Bestimmung der Konstitution der L2. Variegate Periklinalchimären mit Hypodermbildung wurden auf die Möglichkeiten der Bestimmung der L2 hin untersucht. Es werden verschiedene Entstehungsformen von maskierenden Mustern und die noch nicht beschriebenen Ringzellen vorgestellt, die den Idiotyp der L2-bürtigen Schicht anzeigen können. Ringzellen sind die Zellen, die im Bereich der Schließzellen an den substomatären Interzellularraum grenzen. Sie bilden dabei einen Ring um die Schließzellen, der im Flächenschnitt zu erkennen ist. Hypodermale Wasserspeichergewebe sind hauptsächlich bei tropischen Arten verbreitet. Die xeromorphe Struktur kommt sowohl bei den epiphytischen Bromelien als auch bei den hygromorphen Schattenpflanzen des tropischen Regenwaldes vor. Die beiden Selektionsfaktoren Trockenheit und Lichtintensität werden als mögliche Einflussfaktoren auf die Hypodermbildung diskutiert. Beispiele dafür, dass der Faktor Licht auch einen modifikativen Einfluss auf die Differenzierung der Hypodermzellen zu haben scheint, werden vorgestellt. Die Struktur "Hypodermales Wasserspeichergewebe" ist sowohl bei Monokotylen als auch Dikotylen gleichermaßen verbreitet. Es wird daher vermutet, dass es sich um eine analoge Struktur handelt, die mehrmals voneinander unabhängig zu verschiedenen Zeiten bei verschiedenen Arten entstanden ist. Innerhalb einer Gruppe verwandter Arten konnte sie mithilfe der Homologiekriterien als homolog eingestuft werden. / This paper contains three different issues: The structure "hypodermal water storage tissue" is considered from the anatomical, the ecomorphological and evolutionary aspect. Because hypodermal layers are non-green, it is difficult to make a pattern analysis of variegated periclinal chimeras and to determine the constitution of L2. Variegated periclinal chimeras with hypodermal layers were examined to the possibilities of determining L2. Different origins of masking patterns and the non-yet described ring cells are presented. Both structures are able to show the L2-genotype. Ring cells are those cells bordering the intercellular space near the stomata. In a cut parallel to the surface the ring built by ring cells is seen. The hypodermal water storage tissue is mainly distributed among tropical species. The xeromorphic structure occurs both to the epiphytic bromeliads and to the hygromorphic shadow plants of the tropical rainforest. The environmental factors humidity and solar radiation are discussed as possible influences on the development of hypodermal layers. Examples for the apparent modifying influence of solar radiation on the development of hypodermal cells are presented. The structure "hypodermal water storage tissue" occurs both to monocots and dicots. That indicates that it is an analogues structure and that it evolved several times independent of each other in different species. Among a group of nearly related species it could be classified by the aid of the criteria of homology as a homologues structure.