Comparative Wood Anatomy

Convolvulaceae, a large family of worldwide distribution, exhibit a rich diversity of morphological characteristics and ecological habitats. Previous efforts to systematize this diversity without a cladistic phylogenetic framework have disagreed on the circumscription of the family as well as tribal composition and relationship. In order to circumscribe the family and assess the relationships among its major lineages, a broad data set was constructed containing representatives of all ten recognized tribes of Convolvulaceae plus representatives of putatively related families within Asteridae. This is done by using four chloroplast regions: rbcL, atpB, psbE-J operon, and trnL-trnF intron/spacer. The results indicate that Convolvulaceae are monophyletic and sister to Solanaceae. Two of the three groups that have been proposed previously as separate families, Cuscuta and Dichondreae, are nested within the Convolvulaceae in this analysis, and the third, Humbertia, is the sister to all other members of the family. The exact position of Cuscuta could not be ascertained, but some alternatives were rejected with confidence. The study identified several distinct monophyletic groups, some of which correspond to earlier taxonomic treatments. Close relationships of tribes Hildebrandtieae with Cresseae and Ipomoeeae with Argyreieae (forming Echinoconieae) were confirmed. The polyphyly of Merremieae, Convolvuleae, Poraneae, and Erycibeae is first identified in this study.

https://bsapubs.onlinelibrary.wiley.com/doi/epdf/10.3732/ajb.89.9.1510

Monophyly of the Convolvulaceae and circumscription of their major lineages based on DNA sequences of multiple chloroplast loci

Recent advances in wood physiology, molecular phylogeny, and ultrastructure (chiefly scanning electron microscopy, SEM), as well as important new knowledge in traditional fields, provide the basis ...

http://www.sherwincarlquist.com/pdf2/2012_How-Wood-Evolves_2012.pdf

How wood evolves: a new synthesis

Data on wood anatomy are presented in tabular form for 56 sympetalous families of dicotyledons arranged according to the system of Dahlgren, who was influenced by data from presence or absence of iridoids and by embryological information. Each order is reviewed in terms of the degree of correlation of wood data with data from chemistry and embryology. Original data are presented for Buddlejaceae, Globulariaceae, and Selaginaceae. Ericales prove to be a natural and rather primitive group. Cornales as a whole are primitive, but Adoxaceae and Stylidiaceae have distinctively specialized woods (...)

Wood Anatomy of Sympetalous Dicotyledon Families: A Summary, with Comments on Systematic Relationships and Evolution of the Woody Habit

Interxylary phloem is here defined as strands or bands of phloem embedded within the secondary xylem of a stem or root of a plant that has a single vascular cambium. In this definition, interxylary phloem differs from intraxylary phloem, bicollateral bundles, pith bundles, and successive cambia. The inclusive but variously applied terms included phloem and internal phloem must be rejected. Histological aspects of interxylary phloem are reviewed and original data are presented. Topics covered include duration of interxylary phloem; relationship in abundance between sieve tubes in external phloem and interxylary phloem; distinctions between interxylary and intraxylary phloem; presence of parenchyma, fibers, and crystals in the interxylary phloem strands; development of cambia within interxylary phloem strands; three-dimensionalization and longevity of phloem, systematic distribution of interxylary phloem; physiological significance; and habital correlations. No single physiological phenomenon seems to explain all instances of interxylary phloem occurrence, but rapidity and volume of photosynthate transport seem implicated in most instances.

Interxylary phloem: Diversity and functions

Quantitative and qualitative features of wood and stem anatomy are presented for 44 collections of 16 genera and 35 species of Convolvulaceae. Markedly furrowed xylem characterizes the genera of tribe Cresseae. Successive cambia occur in 11 of the genera studied. Large patches of axial parenchyma occur in many of these; only in one species was interxylary phloem (formed internally by the cambium) observed in the parenchyma patches. Intraxylary phloem at the periphery of the pith is universal in Convolvulaceae, but newly reported is the fact that in many species, cambial activity adds secondary phloem to the intraxylary phloem strands. These cambia were also observed to add limited amounts of secondary xylem externally in Ericybe and Operculina. Fragmentation of the vascular cylinder by growth from the inner cambia leads to initiation of radially oriented cambia (ray cambia) along the ray zone where fracture occurs. Three new types of vessel restriction patterns (nonrandom distribution of vessels in wood or absence of vessels within some parts of the secondary xylem) are reported for the family (and dicotyledons). Rays are predominantly uniseriate; ray histology and quantitative vessel features show little change ontogenetically in species with successive cambia, suggesting that this cambial mode deters the kinds ofprogressive changes that occur in dicotyledons with a single cambium. Vessels are much wider in lianoid Convolvulaceae than in shrubby species; the lianoid species of Ipomoea have vessels twice the diameter of those in arborescent species of Ipomoea. Conjunctive parenchyma may serve for water storage in I. arborescens and other species, but this tissue and abundance of axial parenchyma in lianas might also aid flexibility and damage resistance. Septate flber-tracheids and septate libriform fibers occur in a few species and represent tracheid dimorphism. Occurrence of tracheids together with fibriform vessel elements in woods of many Convolvulaceae suggests relationship of Convolvulaceae to Polemoniaceae and Hydrophyllaceae; intraxylary phloem and other wood features suggest relationship between Convolvulaceae and Solanaceae.

/pdf/wood-and-stem-anatomy-of-convolvulaceae-a-survey-g13rdx5190.pdf

Wood and stem anatomy of Convolvulaceae: a survey

Yuccas (Yucca, Agavaceae) are an easily recognizable constituent of the vegetation of the International Four Corners; an area made up of portions of Arizona, New Mexico, Sonora and Chihuahua. We recognize three species as native to the region, Yucca baccata, Y. elata and Y. madrensis, together with interspecific hybrids, and document for the first time naturally occurring intersectional hybridization between baccate-fruited (sect. Yucca) and capsular-fruited (sect. Chaenocarpa) species. We examine the reproductive barriers to hybridization operating within the genus, i.e., spatial, temporal and ethological, and we consider circumstances that may have been responsible for the production and widespread distribution of hybrids in the Il-C. These include establishment of syrnpatry, pollinator biology, founding hybrids and human activities. We also reflect on the present situation regarding sexual reproduction in species of Yucca in the Southwest.

/pdf/yuccas-agavaceae-of-the-international-four-corners-27nrcrtb97.pdf

Yuccas (Agavaceae) of the International Four Corners: Southwestern USA and Northwestern Mexico

George Engelmann 's con cept of Y. schottii as a plant with short, stiff, ye llo w-gree n leaves has not been accepted by recent authors who apply the name to plants of southern Arizona with broad, flexible blue-green leaves. Interspecific hybrids among three yuc ca s present in the area , Y. baccata , Y. elata, and the wide, blue -green leafed plant are co mmo n. We bel ieve that Arthur SChOll'S co llec tions made in 1853 upon which Engelmann based his de scription are of hybrid origin. We accept Engelmann 's designat ion as the earliest applicable binomial but accord it a change in status as Y. x.schottii Engelmann pro , sp. and apply it as a co llective epithet to include all hybrids among the thre e species . We designate Schott 's unnumbered gathering in the Torrey Herbarium (NY) as lectotype. We consider that Y. schottii of authors is con specific with Y. madrensis Gentry of Chihuahua and Sonora , Mexico.

/pdf/typification-and-change-in-status-of-yucca-schottii-2xz6dzj4tp.pdf

Typification and Change in Status of Yucca Schottii (Agavaceae)

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Wood and stem anatomy of Convolvulaceae: a survey

Yuccas (Agavaceae) of the International Four Corners: Southwestern USA and Northwestern Mexico

Typification and Change in Status of Yucca Schottii (Agavaceae)