Registered users receive a variety of benefits including the ability to customize email alerts, create favorite journals list, and save searches.
Please note that a BioOne web account does not automatically grant access to full-text content. An institutional or society member subscription is required to view non-Open Access content.
Contact email@example.com with any questions.
Following his collecting trips to New Caledonia in 1979 and 1981, William C. Dickison published a series of papers focused on the anatomy, morphology, and systematic relationships of the monogeneric, endemic families Strasburgeriaceae, Oncothecaceae, and Paracryphiaceae. He and his collaborators concluded that Paracryphia, Oncotheca, and Strasburgeria should each be treated as distinct families positioned near Sphenostemonaceae, Theaceae, and Ochnaceae, respectively. These anatomical data proved to be a valuable source of systematic characters, but the precise phylogenetic positions of these enigmatic families continue to be in doubt. In fact, even the ordinal classification of flowering plants published by the Angiosperm Phylogeny Group (APG, 1998) left uncertain the position of two of these three families. More recently, however, phylogenies for eudicots based on multiple-gene data sets firmly place Oncothecaceae within Garryales, a position that has never been suggested previously. In the case of Paracryphiaceae, molecular data support the most often cited, historical placement of the family within Dipsacales. New molecular data presented here support the position of Strasburgeriaceae as sister to Ixerbaceae within Crossosomatales. This is one of several historical placements suggested for the family, but a placement that has not been cited in recent years. A comparison of anatomy/morphology between Strasburgeria and Ixerba is presented in the context of this molecular phylogenetic hypothesis.
Basic anatomical features of Cactaceae have been studied since the sixteenth century. This anatomical research has focused on selected features related to different external forms or on stem photosynthetic metabolism. Anatomical stem features, however, have rarely been taken into consideration in systematic studies. Recent work has focused on the subfamily Cactoideae because it is the largest and most diverse subfamily of Cactaceae. Molecular analyses support the monophyly of Cactoideae, but tribal and generic relationships are mostly unresolved. A major goal of this study was to synthesize the available information about anatomical stem features of Cactoideae and to evaluate their usefulness in phylogenetic analysis. Although dermal and vascular tissues have been studied for nearly 350 species of Cactoideae, comprehensive investigations are needed for most members of specific genera or tribes. Phylogenetic analysis based on structural data (morphology and anatomy) showed that the subfamily Cactoideae is monophyletic. This result supports molecular evidence and corroborates that highly reduced leaves are the synapomorphy of this clade. With the exception of Cacteae and Rhipsalideae, the tribes are not monophyletic. The morphological characters that have been used to define the tribes are not synapomorphies and have evolved independently in different lineages. Some anatomical features are unique characters that distinguish terminal taxa; for example, silica grains in dermal and hypodermal cells in Stenocereus, prismatic crystals in dermal and hypodermal cells of Neobuxbaumia, and lack of medullary bundles in members of Cacteae. Most anatomical features, however, behave in a highly homoplasious manner in the analysis of the subfamily. Other studies at the tribal or generic level show that anatomical features are informative and contribute to support different clades. Further studies of Cactoideae, at different taxonomic levels, that include anatomical features, are needed in order to understand their evolution.
More than any other taxonomic character, megaspores have been used in the genus Isoetes (known by the English common name of “quillwort”), despite the fallacy of a single-character taxonomy. Microspores, on the other hand, have been largely neglected in taxonomic schemes. Like megaspores, terms for microspore ornamentation (also known as “sculpturing”) have not been standardized. I examined microspore ornamentation, including both macroornamentation and microornamentation, of 52 taxa from Africa, Asia, Australasia, Europe, North America, and South America with the scanning electron microscope. Macroornamentation is discernible with light microscopy; microornamentation requires scanning electron microscopy. Ornately sculptured spores were much more frequent than were laevigate or psilate patterns: 21 taxa had an echinate pattern; 19 had an aculeate pattern; 6 were cristate; 5 were psilate; and 1 was laevigate. The proximal and distal ridges and surfaces may vary in both the type and density of ornamentation. Distinct macroornamentation patterns characterize certain species groups. Microornamentation types include granulate, bacillate, fimbriate, and filamentose: of the microspores I examined, virtually all were partially granulate; 11 were bacillate; 4 were fimbriate; and 1 was filamentose. Based on this limited sampling, species with a higher ploidy level often have larger microspores, but no clear relationship between microspore ornamentation and ploidy level was established, nor were any geographical or ecological trends clear. Like megaspores, microspore ornamentation is strongly convergent. Although microspores are often attached to megaspores, the role of spore ornamentation in coordinated dispersal remains unclear.
A morphological cladistic analysis is presented of the lilioid order Asparagales, with emphasis on relationships within the “lower” asparagoids, in the context of recent new data on both floral and vegetative structures. The analysis retrieved a monophyletic “lower” asparagoid clade, in contrast to molecular analyses, in which lower asparagoids invariably form a grade. However, limited outgroup sampling in the current analysis is a significant factor in this “inside-out” topology; if the morphological tree is rerooted with Orchidaceae as the outgroup, the result is a topology broadly similar to the molecular one. The relatively low resolution of the “lower” asparagoid clade identified here is a result of high homoplasy in several characters, which could be regarded as iterative evolutionary themes within Asparagales, notably (among floral characters) epigyny and zygomorphy. Close relationships between some family pairs were inferred, including Orchidaceae and Hypoxidaceae, Boryaceae and Blandfordiaceae, Asphodelaceae and Hemerocallidaceae, and Iridaceae and Doryanthaceae. The small South African genus Pauridia, which differs from other Hypoxidaceae in that it lacks the outer stamen whorl, was placed as sister to Orchidaceae rather than being embedded in Hypoxidaceae as in molecular analyses, because despite some significant similarities with other Hypoxidaceae (e.g., mucilage canals), it shares some characters with Orchidaceae, notably the presence of a gynostemium and pontoperculate pollen. Xanthorrhoea and Lanaria were wild-card taxa in the context of this analysis, with characters in common with more than one different group.
Leaf anatomy and petiole anatomy of the Araceae are discussed in terms of their potential use as character states in a phylogenetic analysis. The characters include leaf venation and structure, leaf epidermis, mesophyll ground tissue, vascular bundles, sclerenchyma, collenchyma, laticifers, secretory ducts, and raphide crystals. Characters that seem to have the greatest potential for use in phylogenetic analysis include those of ground tissue, vascular bundles, fibers, trichosclereids, collenchyma, and laticifers. Other, equally distinguishable, characters have states that are apparently autapomorphies, providing little phylogenetic signal. Therefore, although most leaf and petiole structural variation is useful diagnostically, some characters will probably be less valuable in phylogenetic analysis than originally hoped.
Monocotyledons are distinguishable from dicotyledons by their subtype P2 sieve-element plastids containing cuneate protein crystals, a synapomorphic character uniformly present from basal groups through Lilioids to Commelinoids. The dicotyledon genera Asarum and Saruma (Aristolochiaceae-Asaroideae) are the only other taxa with cuneate crystals, but their sieve-element plastids include an additional large polygonal crystal, as is typical of many eumagnoliids. New investigations in Melanthiaceae s.l. revealed the same pattern (polygonal plus cuneate crystals) in the sieve-elementplastids of Japonolirion osense (Japonoliriaceae/Petrosaviaceae), of Harperocalfsflava, Pleea tenuifolia, and Tofieldia (all: Tofieldiaceae). In Narthecium ossifragum a large crystal, present in addition to cuneate ones, usually breaks up into several small crystals, whereas in Aletris glabra and Lophiola americana (Nartheciaceae) and in all of the 15 species studied and belonging to Melanthiaceae s.str. only cuneate crystals are found. Highresolution TEM pictures reveal a crystal substructure that is densely packed in both cuneate and polygonal forms, but in Tofieldiaceae the polygonal crystals stain less densely, probably as a result of the slightly wider spacing of their subunits. The small crystals of Narthecium are “loose”; that is, much more widely spaced. Such “loose” crystals are commonly found in sieve-element plastids of Velloziaceae, present there in addition to angular crystals, and together with cuneate crystals in a few Lilioids and many taxa of Poales (Commelinoids). Ontogenetic studies of the sieve elements of Saruma, Aristolochia, and several monocotyledons have shown that in their plastids cuneate crystals develop very early and independent from a polygonal one present in some taxa. Therefore, a conceivable particulation of polygonal into cuneate crystals is excluded. Consequently, mutations of some monocotyledons that contain a lone, large, polygonal crystal in their sieve-element plastids are explained as the result of a complex genetic block. The total result of all studies in sieve-element plastids suggests that Japonolirion and Tofieldiaceae are the most basal monocotyledons and that Aristolochiaceae are their dicotyledon sister group.
Several ways in which morphology is used in systematic and evolutionary research in angiosperms are shown and illustrated with examples: 1) searches for special structural similarities, which can be used to find hints for hitherto unrecognized relationships in groups with unresolved phylogenetic position; 2) cladistic studies based on morphology and combined morphological and molecular analyses; 3) comparative morphological studies in new, morphologically puzzling clades derived from molecular studies; 4) studies of morphological character evolution, unusual evolutionary directions, and evolutionary lability based on molecular studies; and 5) studies of organ evolution. Conclusions: Goals of comparative morphology have shifted in the present molecular era. Morphology no longer plays the primary role in phylogenetic studies. However, new opportunities for morphology are opening up that were not present in the premolecular era: 1) phylogenetic studies with combined molecular and morphological analyses; 2) reconstruction of the evolution of morphological features based on molecularly derived cladograms; 3) refined analysis of morphological features induced by inconsistencies of previous molecular and molecular phylogenetic analyses; 4) better understanding of morphological features by judgment in a wider biological context; 5) increased potential for including fossils in morphological analyses; and 6) exploration of the evolution of morphological traits by integration of comparative structural and molecular developmental genetic aspects (Evo-Devo); this field is still in its infancy in botany; its advancement is one of the major goals of evolutionary botany.
William Campbell Dickison, professor of biology at the University of North Carolina at Chapel Hill and internationally noted plant anatomist and morphologist, died on 22 November 1999. This tribute chronicles his life journey and elucidates his accomplishments in and contributions to botany.
William Campbell Dickison (Fig. 1) was a plant anatomist and morphologist of international distinction. His life journey took him to the Gulfport-Biloxi, Mississippi, region, to Des Plaines and Macomb, Illinois, to the Bloomington campus of Indiana University, to the deserts of Arizona, to the mountains of Virginia, and finally to the North Carolina college town of Chapel Hill. He was influenced by experiences in each of these settings. This biographical tribute greatly expands on insights of BilI's life and accomplishments given by Gensel (2000), Wheeler (2000), White (2000), and Burk (2001).
Even though William C. Dickison was weakened by his long battle against bonemarrow cancer, he was reading final page proofs and making text corrections for his new book on plant anatomy up to his last days. In fact, he maintained an optimistic outlook that extended beyond this publishing venture, as confirmed by discussions he had with a close colleague about his desire to write a textbook on plant diversity. Although Bill was first diagnosed with cancer in the spring of 1992, few of us knew that he was ill until the affects of his medical treatments became apparent. His dedication to research in plant anatomy and morphology prevailed, and his commitment to teaching continued until just weeks before his untimely death on 22 November 1999. The botanical and academic community has lost a genuine scholar and compassionate friend. His legacy includes landmark publications that will influence the thinking of present and future botanists and scholastic ideals that will live on through those who were associated with him.