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The Lythraceae (Myrtales) are a family of 28 genera and ca. 600 species constituting with the Combretaceae and sister family Onagraceae a major lineage of the Myrtales and including the former Sonneratiaceae, Duabangaceae, Punicaceae, and Trapaceae. The fossil record of the family is extensive and significant new discoveries have been added to the record in recent years. This review provides a vetted summary of fossils attributed to the Lythraceae, their geographic distributions, and their stratigraphic ranges. It anticipates the use of the information to generate robustly dated molecular phylogenies to accurately reconstruct the evolutionary and biogeographic history of the family. Fossils of 44 genera or form genera have been attributed to the Lythraceae; 24 are accepted here as lythracean. Fourteen of the 28 modern genera have fossil representatives: Adenaria, Crenea, Cuphea, Decodon, Duabanga, Lafoensia, Lagerstroemia, Lawsonia, Lythrum, Pemphis, Punica, Sonneratia, Trapa, and Woodfordia. Ten extinct genera are recognized. The most common kinds of fossil remains are seeds and pollen. The only fossil flower confidently accepted in the family is the extinct genus Sahnianthus from the Early Paleocene of India. The oldest confirmed evidence of the Lythraceae is pollen of Lythrum/Peplis from the Late Cretaceous (early Campanian, 82−81 Ma) of Wyoming. Seeds of Decodon from the late Campanian (73.5 Ma) of northern Mexico are next oldest. Sonneratia, Lagerstroemia, and extinct Sahnianthus first appear in the Paleocene of the Indian subcontinent; extinct Hemitrapa fruits first occur in the Paleocene of northwestern North America. Diversification of the Lythraceae occurred primarily during two major periods of global temperature change, during the Paleocene-Eocene Thermal Maximum and from the middle Miocene forward when temperatures decreased markedly and seasonality and dry-adapted vegetation types became more prominent. Fossils of the Lythraceae from South America and Africa are limited in number. The few dates available for South American genera are comparatively young and diversification of the largest genus, Cuphea (ca. 240 species), was mainly a Quaternary event. A phylogeny of the family is briefly explored and examples of specialized characters occurring in the oldest known genera are noted. The fossil record of the Lythraceae is presently too fragmentary to confidently reconstruct the early history of the family. The record indicates, however, that the family was well-diversified and widely dispersed globally over a wide latitudinal range by the end of the Paleocene.

Phylogenetic relationships of Lythraceae sensu lato (s.l.) were investigated by parsimony and likelihood analyses of 85 accessions representing 23 species, 16 genera that have been assigned to the family at various times. The three data sets, including the chloroplast rbcL gene, the psaA‐ycf3 spacer, and the nuclear internal transcribed spacer (ITS; including the 5.8S ribosomal gene), are highly congruent on the basis of the partition homogeneity test. No significantly long branches are detected by relative apparent synapomorphy analysis. Phylogenetic analyses based on the combined data strongly support the monophyly of the Lythraceae s.l., in which the satellite genera Dubanga, Punica, Sonneratia, and Trapa were included, with Onagraceae and Combretaceae as outgroups. Paraphyly of subfamily Lythroideae (= Lythraceae sensu stricto) is proposed with the other four monotypic subfamilies nested within. The analysis further supports the sister relationship between Sonneratia and Trapa instead of Duabanga and ...

nested within the Sonneratiaceae. The Sonneratiaceae occurred within the Lythraceae with high bootstrap value support (96%). The two traditional genera constituting Sonneratiaceae were in different well-supported clades. Duabanga (Sonneratiaceae) is sister to the clade of Lagerstroemia (Lythraceae) (82%). The mangrove genus Sonneratia (100%) formed the other monophyletic group. It was located terminally within the Lythraceae clade and comprised two clades: one consisting of S. apetala, S. alba, S. ovata, and S. hainanensis; the other including S. caseolaris and S. paracaseolaris. The results indicated that species previously placed in two different sections (Sect. Sonneratia and Sect. Pseudosonneratia) of Sonneratia occurred within the same clade, and the taxonomic classification was not supported by the molecular analysis of the ITS region sequences. Based on the phylogenetic analyses of the ITS regions, the Sonneratiaceae were shown to be nested within the family Lythraceae. Therefore, the sequence data presented here do not support the recognition of the Sonneratiaceae as a distinct family, but instead support the inclusion of Sonneratiaceae in the Lythraceae proposed by other authors.

A permineralized lythraceous leaf type found in close association with fruits, stems, and roots of Decodon allenbyensis Cevallos-Ferriz et Stockey in the Middle Eocene Princeton chert of British Columbia, Canada, is described. Midribs have a prominent C-shaped midvein surrounded by sclerenchyma, with an adaxial epidermis of rectangular to rounded cells lacking enlarged mucilage cells. Leaves are dorsiventral, 180-270 micrometer thick at the lamina, with a double palisade layer. Abaxial epidermal cells have prominent papillae, and these epidermal cells can be infected by fungi, forming dark sterile stromata. Fossil leaves are similar to those of Myrtales and are compared to those of Lythraceae sensu lato. Although these leaves are thought to belong to the previously described Decodon allenbyensis found in the same chert layer, they lack the diagnostic features of extant Decodon leaves. Instead they share most anatomical similarities with Duabanga grandiflora Roxburgh ex DC Walpers (Lythraceae, subfamily Duabangoideae) including vascular tissues, palisade and spongy mesophyll, bundle fibers, and abaxial epidermal papillae. Duabanga grandiflora differs from the fossil in having mucilaginous cells and a consistently V-shaped abaxial midrib. Although anatomically similar to Duabanga, the fossil leaves are considered those of D. allenbyensis, based on association and the depositional environment prior to preservation. Recent phylogenetic analyses place Duabanga and Decodon in separate clades within Lythraceae, but relationships between these clades are not well supported, indicating that fossil leaves should provide useful anatomical characters for elucidating relationships within Lythraceae.

GRAHAM, S. A., CRISCI, J. V. & HOCH, P. C, 1993. Cladistic analysis of the Lythraceae sensu lato based on morphological characters. The Lythraceae s. I. comprise 31 mostly highly distinctive genera distributed worldwide. Cladistic analyses of the family were undertaken using 26 characters from anatomy, floral morphology, pollen, and seed morphology. Of four outgroup hypotheses, the Onagraceae offered the best heuristic assessment, generating 3746 trees with a tree length of 83 and consistency index and (C.I.) of 0.41. A strict consensus tree from the 3746 trees produced a basal monophyletic group of five genera (Sonneratia, Duabanga, Punka, Lagerstroemia, Lawsonia) characterized by anthotelic (determinate) inflorescences and wet stigmas, and a second clade with blastotelic (indeterminate) inflorescences, dry stigmas, and reduced carpel number. Successive weighting with Onagraceae as outgroup generated five most parsimonious trees with a tree length of 164 and C.I. of 0.75. Internal branches are weakly supported by only seven non-homoplasious characters. Significant results of the analysis include: (1) recognition of the two major clades and a total of seven monophyletic groups within the family; (2) the paraphyly of subfamily Lythroideae (Lythraceae s. s.); and (3) indication that genera endemic to the New World have been derived from more than one ancient Old World evolutionary line. The current taxonomic classification of the family is not closely correlated with results of the cladistic analysis.

Published chromosome numbers in Sonneratia and Duabanga are inconsistent and indicate the basic numbers of the two genera are x = 9 or 11 and x = 12, respectively. Chromosome number counts made in this study for three species of Sonneratia indicate 2n = 24, and for two species of Duabanga, 2n = 48. The base is established as x = 12 in both genera. Although the genera have accumulated numerous autapomorphies that lead them to be regarded in separate subfamilies Sonneratioideae and Duabangoideae of the Lythraceae s.l., they share karyologically similar chromosomes and a unique basic number for the family, which is x = 8 in the remaining subfamilies Punicoideae and Lythroideae. Sonneratia and Duabanga are regarded as among the most primitive genera of the Lythraceae s.l. A number of other myrtalean higher taxa also have x = 12. This base number is most likely the ancestral number for the order.

Summary Chromosome numbers of 12 genera and 13 species of the Lythraceae sens. str. were determined. Nine of 12 genera and 12 species are reported for the first time. An analysis of all published chromosome data including these new counts shows that 13 of 15 genera for which we could determine the base number have x = 8, and two remaining genera (Peplis and Lythrum) x = 5, thus confirming an earlier suggestion that the original basic number of the Lythraceae is x = 8. On the basis of evidence from chromosome number alone, Punica (x = 8) (Punicaceae) fits in well with the pattern of chromosome numbers in the Lythraceae, but Sonneratia (x = 9 or 11) and Duabanga (x = 12) (Sonneratiaceae) are more distinct and perhaps derived from a group ancestral to modern Lythraceae.

The wood anatomy of Duabanga and Sonneratia is described in detail. Based on the present investigation as well as on the well recognised differences between these two genera, their systematic position is discussed. The study endorses the suggestion made by Dahlgren and Thorne (1984) to raise the status of these two genera to two subfamilies within the Lythraceae. The ecological differences between these two genera in relation to their xylem anatomy is also discussed.

Pollen of the 27 genera presently recognized as comprising the family Lythraceae have been surveyed with light microscopy and scanning and transmission electron microscopy. Results for five genera (Physocalymma, Pleurophora, Rotala, Tetrataxis, Woodfordia), in addition to Duabanga, Sonneratia, and Punica (assigned to the Lythraceae in some classifications), are presented here; the remaining genera were treated previously in the series. The family is revealed as the most diverse palynologically of the order Myrtales. The most simple pollen type and the one common to the largest number of genera is prolate-spheroidal to prolate; tricolporate, without pseudocolpi; psilate, scabrate or finely verrucate; and 16-28 μm or less in length. Specializations include oblate grains, development of pseudocolpi (three or six in number), diversification of exine sculpturing, broadening of the colpal and pseudocolpal areas, and reduction in the conspicuousness of the colpi. Pollen evidence provides qualified support for inclusion of Punica in the Lythraceae, the generalized nature of the pollen tempering the conclusion, and little support for inclusion of Sonneratia and Duabanga in the family. Completion of the survey provides a data base of pollen characters that will be integrated in future studies with other evidence into an overall phenetic and cladistic assessment of the family leading to production of a more natural classification.