Natalie W. Uhl

Complete Generic-Level Phylogenetic Analyses of Palms (Arecaceae) with Comparisons of Supertree and Supermatrix Approaches

Supertree and supermatrix methods have great potential in the quest to build the tree of life and yet they remain controversial, with most workers opting for one approach or the other, but rarely both. Here, we employed both methods to construct phylogenetic trees of all genera of palms (Arecaceae/Palmae), an iconic angiosperm family of great economic importance. We assembled a supermatrix consisting of 16 partitions, comprising DNA sequence data, plastid restriction fragment length polymorphism data, and morphological data for all genera, from which a highly resolved and well-supported phylogenetic tree was built despite abundant missing data. To construct supertrees, we used variants of matrix representation with parsimony (MRP) analysis based on input trees generated directly from subsamples of the supermatrix. All supertrees were highly resolved. Standard MRP with bootstrap-weighted matrix elements performed most effectively in this case, generating trees with the greatest congruence with the supermatrix tree and fewest clades unsupported by any input tree. Nonindependence due to input trees based on combinations of data partitions was an acceptable trade-off for improvements in supertree performance. Irreversible MRP and the use of strictly independent input trees only provided no obvious benefits. Contrary to previous claims, we found that unsupported clades are not infrequent under some MRP implementations, with up to 13% of clades lacking support from any input tree in some irreversible MRP supertrees. To build a formal synthesis, we assessed the cross-corroboration between supermatrix trees and the variant supertrees using semistrict consensus, enumerating shared clades and compatible clades. The semistrict consensus of the supermatrix tree and the most congruent supertree contained 160 clades (of a maximum of 204), 137 of which were present in both trees. The relationships recovered by these trees strongly support the current phylogenetic classification of palms. We evaluate 2 composite supertree support measures (rQS and V) and conclude that it is more informative to report numbers of input trees that support or conflict with a given supertree clade. This study demonstrates that supertree and supermatrix methods can provide effective, explicit, and complimentary mechanisms for synthesizing disjointed phylogenetic evidence while emphasizing the need for further refinement of supertree methods.

Major trends of evolution in palms

From the diversity found among palms the following evolutionary trends are suggested:habit: from sympodial to monopodial;size: from moderate toward large and also toward small;stem: from unbranched to dichotomously branched, from little to much sclerenchyma, from short to elongate internodes;leaf: from an undivided eophyll to a palmate, costapalmate, pinnately ribbed or pinnate blade; from undivided and plicate to divided along the adaxial rib (“induplicate”) or along the abaxial rib (“reduplicate”); from pinnate to bipinnate or to pinnae onceor twicedivided longitudinally; from sheath split opposite the petiole to sheath tubular; from marcescent to deciduous; from central vascular bundles of the petiole with a single phloem strand to two phloem strands;inflorescence units: from moderately branched to spicate or less frequently to more diffusely branched, from one unit per leaf axil to more than one per axil, from among the leaves to below them or to above them in a compound terminal inflorescence, from pleonanthic to hapaxanthic;prophyll: from completely to incompletely encircling the peduncle, from incompletely to completely sheathing in bud;bracts: from conspicuous to small or absent at maturity, first peduncular bract from tubular and open at the apex to completely enclosing the inflorescence in bud, and then from ungrooved to deeply plicate;flower arrangement: from solitary, pedicellate, bracteolate flowers to a sympodial cincinnus of 2 or 3 or more, or to a short monopodial axis of 2–4 or more;bracteoles: from sheathing and prophyllate to completely closed or to incompletely developed or absent;flowers: from bisexual to unisexual, then associated with polygamy or monoecism to dioecism;perianth: from trimery to dimery or tetramery to decamery or to reduced and monochlamydeous;sepals: from distinct and imbricate to connate or separated;petals: from distinct and imbricate to valvate, or strongly imbricate, or connate; from small and ovate to large and variously shaped, or to small;stamens: from 6 to 3 or to more than 6 (to 950+);filaments: from relatively slender and distinct to broad and thick, and often connate or adnate to the perianth or both;staminodes: from stamenlike with abortive anthers only, to short teeth, or to a cupule at the base of the ovary, or to absent;pollen: from monosulcate to trichotomosulcate to dicolpate to monocolpate, diporate, or triporate;gynoecium: from apocarpous to syncarpous, from thin walls to thick, variously specialized walls;carpels or locules: from 3 to 2-1 or to 4–10;ovules: from moderate to small or to large, from anatropous to hemianatropous to campylotropous to orthotropous;pistillode: from only slightly modified from the gynoecium to vestigial or lacking or rarely to prominent;fruit: from fleshy to dry and fibrous;endocarp: from little differentiated or thin, to thick and hard, and sometimes with a pore or operculum over the embryo;seed: from moderate to small or to very large, from entire to dissected, bilobed, or perforate;endosperm: from homogeneous to invaginated or ruminate;germination: from remotetubular or -ligular to adjacent-ligular;chromosome complement: fromn = 18 ton = 17, 16, 15, 14, 13.ResuméDe la diversité trouvée parmi les palmiers les tendances évolutives suivantes sont suggérer:croissance: de sympodique à monopodique;taille: de médiocre à grande et aussi à petite;tige: de non branchée à divisée en branches dichotomes, de peu de sclerenchyme à beaucoup, de entrenoeuds courts à allongés;feuille: d’une eophylle entière à une limbe palmée, costapalmée, à nervures pennées, ou pennée, de tout entière et plicative à divisée le long des nervures adaxiales (“indupliquée”) ou des nervures abaxiales (“redupliquée”), de pennée à bipennée ou les folioles divisées longitudinalement une ou deux fois, de gaîne fendue de l’autre coté du pétiole à tabulaire, de marcescente à caduque, d’un faisceau du liber solitaire à faisceaux deux;unités de la inflorescence: de ramifiées modérément à spiciforme ou moins souvent à ramifiées plus diffusément, d’une unite seule par axille d’une feuille à plus d’unités par axille, de émergentes parmi les feuilles à émergentes au-dessous d’elles ou à émergentes au-dessus d’elles en une inflorescence composée, de pléonanthiques à hapaxanthiques;prophylle: de complètement à incomplètement ceignante le pédoncle, de incomplètement à complètement engainante la inflorescence bourgeonnée;bractées: de bien visible à petites ou absentes à maturité, la premier bractée pédonculaire de tubulaire et ouverte au sommet à complètement entourante la inflorescence bourgeonnée, et dans ce dernier cas de non cannalée à profondément plicative;disposition des fleurs: fleurs de solitaires, pédicellées, bractéolées à disposées en deux ou trois ou plus en cincinnus sympodique, ou à disposées en deux à quatre ou plus en un court axe monopodique;bractéoles: d’engainantes et prophylloides à complètement fermées ou à incomplètement développées ou absentes;fleurs: de bissexuelles à unisexuelles, et dans ce dernier cas associées en état polygame ou monoiïque a dioïque;périanthe: de trimère à dimère ou tetramère à decamère ou réduite et monochlamydée;sépales: de distincts et imbriqués à connés ou séparés;pétales: de distincts et imbriqués à valvés, ou fortement imbriqués, ou connés, de petits et ovales à grands et diversement formés, ou à petits;étamines: de 6 à 3 ou à plus que 6 (à 950+);filets: de relativement minces et distincts à larges et épais et souvent connés ou adnés à la périanthe, ou tous deux;staminodes: de staminiformes avec anthères abortives, à dents courtes, ou à une cupule à la base du ovaire, ou à absentes;pollen: de “monosulcate” à “trichotomosulcate” à dicolporé à monocolporé, diporé, ou triporé;gynécée: de apocarpée à syncarpée, avec parois de minces à épaisses et diversement specializées;carpelles ou locules: de 3 à 2-1 ou à 4–10;ovules: de médiocres à petits ou à grands, de anatropes à hemianatropes à campylotropes à orthotropes;pistillode: seulement légèrement modifier de la gynécée, à vestigiale ou absente ou rarement à saillante;fruit: de charnu à sec à fibreux;endocarpe: de légèrement différencié ou mince, à épais et dur, et quelouefois avec un pore ou un opercule au-dessus de l’embryon;graine: de médiocre à petite ou à très grande, de entière à découpée, bilobée, ou perforée;endosperme: de homogène à envaginé ou ruminé;germination: de éloigné-tubulaire ou-ligulée à adjacent-ligulé;complément de chromosomes: den = 18 àn = 17, 16, 15, 14, 13.

Palms and the Origin and Evolution of Monocotyledons

Past and Present taxonomic treatments and evolutionary analyses of monocotyledons have noted that unspecialized reproductive structures occur in some palms, but the size, inaccessibility, apparent and often real complexity of these plants have hampered detailed studies until recently. The most primitive palms are 14 or 15 apocarpous genera belonging to the Trithrinaux alliance in the coryphoid group. Apocarpy also characterizes Phoenix, a genus related to coryphoid palms but more specialized in some respects, and Nypa fruticans, a mangrove palm with a unique combination of primitive and specialized features. Distribution patterns, habits, leaf structure, germination, reproductive structures, chromosomes numbers, vessels, and vascular systems are described, as presently known, in these primitive palms, and their significance in the evolution of other palms, monocotyledons, and dicotyledons is evaluated. It is concluded that the palsm are not a morphologically unique and isolated group, as often postulated, but that they frequently express most clearly evolutionary sequences fundamental to monocotyledons as a whole. Evolution in palms substantiates a number of different evolutionary sequences in monocotyledons and dicotyledons, and suggests other possibly different trends for investigation. The review provides evidence that the exploitation of different evolutionary sequences by monocotyledons and dicotyledons necessitates separate consideration of evolution within each class of angiosperms. It is suggested that an early divergence of monocotyledons and dicotyledons from protoangiosperms or perhaps even from preangiosperms may be compared to the evolution of birds and mammals from diverse reptilian groups.

Floral development in Aphandra (Arecaceae)

The organogenesis of staminate flower clusters and flowers and some observations on the corresponding pistillate structures of Aphandra natalia are described and compared with those of the other two genera in the Phytelephantoideae (Arecaceae). In Aphandra, staminate flowers are borne in monopodial clusters of mostly four (1-6) flowers. Each flower is surrounded by two pairs of subopposite bracteoles and has two rather indistinctly four-parted whorls of perianth parts. Stamen primordia arise on a shallow apical dome and then centrifugally down the sides of a long, angled, and laterally flattened receptacle. Immediately before the staminate bud opens, the floral receptacle below the androecium rapidly elongates, becoming funnel-shaped, with the bracteoles and a perianth sheath adnate to it forming a pseudopedicel. Epidermal and subepidermal layers of these pseudopedicels split at anthesis and release a great number of raphide idioblasts that resemble the pollen grains in shape and size. It is hypothesized that the idioblasts deter pollen feeding or ovidepositing insects. The phylogenetic implications of these findings are important within the Phytelephantoideae and among palms in general.