| # The families of flowering plants |

L. Watson and M.J. Dallwitz

## Introduction

This interactive package is generated from a DELTA database (Dallwitz 1980; Dallwitz, Paine, and Zurcher 1993). It comprises an interactive system for identification and information retrieval using the program Intkey (Dallwitz, Paine, and Zurcher 1995, 2000), along with descriptions, illustrations, references, and other subsidiary material. In addition to this version, the full family descriptions are available as Web pages, with diagnostic attributes highlighted.

The reasons for preparing automated descriptions of Angiosperm families, the intended applications for which the database was designed, and the rationale for the manner of its construction, were set out in detail when it was first released (Watson and Dallwitz 1991). The principal objectives were (1), to facilitate direct comparisons of rival familial and supra-familial classifications, in terms of the comparative descriptive data on which taxonomy is expected to impose meaningful patterns; (2), to assist with choosing appropriate samples for taxonomically orientated nucleic acid sequencing; and (3), to assist such potential users of taxonomic systems as physiologists, biochemists and geneticists to select informative, taxonomically balanced samples for experimental work. Hence, with inevitable qualifications (see below) the current package purports to include every family of at least some taxonomic merit. While there is scope for improvement, it offers for each of them a morphological description that is at least workable for identification, although some are minimal even for that purpose. Also included are family synonyms; information on numbers of species and genera in each family, and lists of the genera in each.

Information is included on geographical distributions, on variation in photosynthetic pathways (with lists of the genera known to include C4 and/or CAM species), and on the occurrence of leaf phloem transfer cells (the latter summarizing primary data not published elsewhere); and compiled data are also included on other features, including seedling germination type, embryology, anther ontogeny, pollen cytology and morphology, stigma type, sieve-tube plastids, leaf, stem, nodal and wood anatomy, and phytochemistry (phenolics, alkaloids, cyanogenesis, etc.). Inclusion of comparative data on such ‘esoteric’ characters is essential, in view of the acknowledged importance and future potential of reciprocal exchanges of information between taxonomy and other disciplines. Perusal of the References will show that much of the data on them requires updating, and contributions in that connection will be gratefully received. Many of the works listed are largely or partly compilations, which themselves cite primary data sources: the latter are listed only when they have been utilized directly.

Buttons in the Intkey toolbars permit selecting subsets of characters and taxa for efficient identification (geographical subsets, fragmentary material, fossils, etc.). It is also easy, using Intkey, to obtain lists of families exhibiting or lacking particular features or combinations of features; to cross reference attributes with geographical distributions and classifications; to compare rival family classifications in terms of group contents, and in terms of the available descriptive data (with statistical details of character state distributions); to obtain lists of families for which information on particular features is lacking; to locate family synonyms, and assign generic names to families; and to obtain printouts of all such information.

### Family circumscriptions and classification

Narrow family circumscriptions, mainly as exemplified by Airy Shaw (1973), were deliberately employed here. These are preferable in the present context both to the broader interpretations of Cronquist (1988; see also Mabberley 1989) and to those now being proposed with increasing frequency (and sometimes with shallow justification) on cladistic grounds, because they better indicate the extent of sampling in relation to ‘esoteric’ characters, many of which are of considerable taxonomic and/or economic interest. Furthermore, the elevated levels of internal variation exhibited by sensu lato descriptions sometimes preclude effective family diagnoses, can be unpractical for pursuing identifications, and pose serious problems for classificatory and cladistic morphological analyses of the data. It is impracticable in any case to offer family descriptions fully in line with current views on Angiosperm phylogeny espoused by the APG and other practitioners of cladistics, because many re-circumscriptions are published without properly revised descriptions. The requisite data would have to be laboriously extracted from a mountain of publications, most of which purvey non-comparative and often hopelessly incomplete descriptive information. Such products are unlikely to be taxonomically definitive, and in any case are useless in practice, because properly revised descriptions are essential for practical implementation in floras. However, should sensu lato descriptions be required, they are very easily generated automatically from our sensu stricto versions, complete with statistical distributions of character states, by applying Intkey to the data in this package.

At supra-familial levels, we currently incorporate the complete classifications, to the level of Order, of Dahlgren (1980), Cronquist (1981) for Dicots, and of Dahlgren, Clifford and Yeo (1985) for Monocots; comprehensive assignment of Dicotyledons to the Crassinucelli and Tenuinucelli of Young and Watson (1970); and the APG III (2009) classification of Flowering Plants into formal and informal supra-ordinal groups and Orders. As exemplified in the accompanying Notes on the APG classification, their inclusion renders it easy, using Intkey, to directly compare rival classifications, both in terms of group family contents and of character state distributions across the groups. DNA sequencing studies from 1993 onwards are providing exciting new phylogenetic and classificatory insights, but definitive taxonomic conclusions will demand congruent results from DNA comparisons (nuclear, as well as chloroplast) which can reasonably be expected to represent whole plant genomes, as well as thorough sampling of genera and species. They will not be achieved by sequencing one or two genes, and phylogenies based entirely on plastid DNA in particular do not inspire confidence unless the results are consistent with other comparative data. Furthermore, little or no attention appears to have been paid to likely past occurrences in plants of lateral transfer of genetic material at high hierarchical levels, for example through the agencies of parasitic bacteria, fungi and viruses. Meanwhile, a commonsense approach to assessing the worth of purported phylogenies and revised classifications requires setting them against properly organized, comparative descriptive data of the kind offered in this package.

### Illustrations

The package includes numerous, copyright free illustrations of both taxa and characters, with many families represented by several ‘technical taxonomic’ images, and many character states exemplified by several images in an attempt to indicate the ranges of variation encompass. The ‘technical taxonomic’ images have been supplemented, with Zoya Akulova’s permission, by selections of photographs from her recent postings at calphotos.berkeley.edu.

The numerous line drawings accompanying earlier versions of the package were mainly from Le Maout and Decaisne’s A General System of Botany (1873: illustrated by L. Steinheil and A. Riocreux, who used Decaisne’s collection of analytical drawings), Lindley’s The Vegetable Kingdom (1853: illustrations specially prepared for that work, or from other sources specified on the legends), Thonner’s Flowering Plants of Africa (1915), and (for vegetative anatomy) Solereder’s Systematic anatomy of the Dicotyedons. Apart from a few original photographs, the very numerous subsequent additions – comprise high resolution scans of hand-coloured engravings from Watson’s copy of John Curtis’s British Entomology;; also by adapted scans of numerous tecnically informative plates from volumes 1-146 of the Botanical Magazine (commenced by William Curtis, 1790-1920), mostly downloaded from the excellent Biodiversity Library (www.biodiversitylibrary.org/); from volumes 1–14 (1815–1828) of the Edwards and Ridgeway Botanical Register, from the third (1863) edition of the Sowerby et al. English Botany, from R. Wight’s excellent Illustrations of Indian Botany (1840 and 1850) and the Hooker et al. Icones Plantarum (1837–1922); also numerous line drawings from Hutchinson (1959). Illustrations in Intkey displays are succinctly referenced in the headings, and details of major sources are available in the References file. Much effort has been expended in cleaning up the scanned images, re-arranging material as depicted in the originals to conserve space, pasting on the original legends as necessary, and scaling the products as appropriate for screen display. It seemed unnecessary in the present context to reword original legends, which sometimes carry superseded generic names; but identities and nomenclature have been laboriously updated for the Intkey package via modern floras, the Kew Plant List (http://www.theplantlist.org) and most recently the World Flora Online (http://www.worldfloraonline.org); cf. our References file, and the headings and notes offered with Intkey displays of taxon images. Our ‘Updated plant names for John Curtis’s British Entomology (1824–1840)’ comprises a comprehensive, nomenclaturally updated list of the plant illustrations accompanying those of the insects in that splendid work.

Revised 28 December 2019

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