Abstract Detail

Anatomy and Morphology

L. Cunha Neto, Israel [1], Pace, Marcelo [2], Douglas, Norman [3], Moore, Michael [4], Angyalossy, Veronica [1].

Development and diversity of primary vascular system and its implications for the systematics and evolution of Nyctaginaceae.

The Nyctaginaceae include ca. 400 species within 31 genera divided in seven tribes. The species vary from shrubs to trees, herbs, lianas, and subshrubs. This wide range of habits was accompanied by a large diversity in the vascular system architecture. The occurrence of medullary bundles – which is directly related to the stele characterization – is one of the most remarkable features of the family. However, their ontogeny is still poorly understood, and their diversity and distribution has not been studied under a phylogenetic framework. In order to understand their anatomy and evolution and other aspects of the primary vascular system within Nyctaginaceae we have carried out a comparative study broadly sampling taxa within the family, mostly from plants growing in their natural habitats. So far, 59 species have been sampled, distributed in 24 genera and 6 tribes. After thorough developmental and structural analyses, we then reconstructed the history of medullary bundles using a well-supported phylogeny of the family, as well as its sister lineages (Agdestidaceae, Sarcobataceae, Petiveriaceae and Phytolaccaceae). Based on the occurrence and distribution of medullary bundles in Nyctaginaceae, we find two types of stele in the family, the polycyclic eustele (containing medullary bundles) and regular eustele (without medullary bundles). The observed distribution of the two characters states is enough to define an entire clade, since the regular eustele is exclusive to all the representatives of tribe Lecaustereae. Medullary bundles are formed in earlier stages of development departing from leaf-traces – and other lateral appendages, such as thorns and branches – constituting the first primary vascular tissue to be established. Although the origin and development of the medullary system is uniform across the taxa, the number and arrangement of medullary bundles within the pith is variable. The phylogenetic reconstruction of the eustele characters within Nyctaginaceae recovered that the ancestors for the family had medullary bundles (polycyclic eustele). As a result, the occurrence of regular eustele in tribe Leucastereae represents a single evolution (autapomorphy) within the Nyctaginaceae, whereas the presence of medullary bundles in the remaining taxa represent a symplesiomorphy for the rest of the family. Given that the character state ancestral for all lygnophytes is reconstructed as a regular eustele, the presence of regular eustele in tribe Leucastereae represents a reversal (an independent evolution), whereas the presence of medullary bundles in the remaining taxa (Nyctaginaceae + sister lineages) would represent a synapomorphy to this larger clade within the Caryophyllales.

1 - University of São Paulo, 277 Matao st., Instituto de Biociências, São Paulo, SP, 05508-090, Brazil
2 - Universidad Nacional Autónoma de México, Biology, Edificio A, Piso 2: 217, Mexico City, MX
3 - University Of Florida, Biology, PO Box 118525, Gainesville, FL, 32611, United States
4 - Oberlin College, Department Of Biology, 119 Woodland St., Science Center K111, Oberlin, OH, 44074, United States

Keywords:
anatomy
Caryophyllales
medullary bundles
phylogeny
evolution.

Presentation Type: Oral Paper
Session: AM2, Anatomy and Morphology II
Location: San Ignacio/Starr Pass
Date: Tuesday, July 30th, 2019
Time: 2:15 PM
Number: AM2004
Abstract ID:610
Candidate for Awards:Katherine Esau Award,Maynard F. Moseley Award