The families of flowering plants
Habit and leaf form. Submerged, brittle, rootless aquatic herbs (the plant decaying behind as it grows in front). Plants rootless. Without conspicuous aggregations of leaves. Hydrophytic; free floating. Leaves submerged. Leaves small to medium-sized; whorled; 3–10 per whorl; becoming brittle with age; petiolate; ambiguously interpretable as simple, or compound. Lamina dissected; once or twice finely dichotomously dissected. Leaves exstipulate.
Leaf anatomy. The leaf lamina centric (elliptical or circular in section, with a single vascular bundle devoid of vessels and surrounded by a parenchymatous sheath, the epidermis containing more chloroplasts than the mesophyll and the latter traversed longitudinally by large air canals). Stomata absent. Hairs present; eglandular and glandular (the apices of the segments bearing long, multiseriate shaggy glands, filled when young with oily, rose-coloured myriophyllin and later with tannin; each gland accompanied on either side by a long, pointed unicellular hair). Minor leaf veins without phloem transfer cells.
Axial (stem, wood) anatomy. Cork cambium absent. Primary vascular tissues consisting of a single vascular strand occupied by an axile air canal surrounded by elongated amyliferous cells representing xylem, this in turn surrounded by two rings of wide sieve tubes and companion cells embedded in parenchyma: see illustration. Secondary thickening absent. The axial xylem without vessels.
Reproductive type, pollination. Plants monoecious. Female flowers without staminodes. Pollination by water.
Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in inflorescences (one per leaf axil, in whorls!); axillary; ebracteate; ebracteolate; minute; regular; cyclic (female), or partially acyclic (male). The androecium acyclic. Hypogynous disk absent.
Perianth sepaline (bractlike); 9–10; joined (basally); 1 whorled.
Androecium (5–)10–20(–27) (in male flowers). Androecial members free of the perianth; all equal; free of one another. Androecium exclusively of fertile stamens. Stamens (5–)10–20(–27); filantherous to with sessile anthers (subsessile). Anthers adnate; non-versatile; dehiscing irregularly, or dehiscing via longitudinal slits; extrorse; appendaged (via the often coloured, apically projecting connective). The anther appendages apical. Microsporogenesis successive, or simultaneous. Tapetum amoeboid, or glandular. Pollen shed as single grains. Pollen grains nonaperturate; 2-celled.
Gynoecium in female flowers 1 carpelled. The pistil 1 celled. Gynoecium monomerous; of one carpel; superior. Carpel stylate; apically stigmatic; 1 ovuled. Placentation apical. Ovules pendulous; non-arillate; orthotropous; unitegmic; crassinucellate. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; small. Hypostase present. Endosperm formation cellular. Embryogeny asterad.
Fruit non-fleshy. The fruiting carpel indehiscent; an achene. Seeds non-endospermic. Embryo well differentiated (but without a functional radicle). Cotyledons 2. Embryo chlorophyllous (fleshy); straight.
Seedling. Germination phanerocotylar.
Physiology, phytochemistry. Not cyanogenic. Proanthocyanidins present; cyanidin and delphinidin. Flavonols absent. Ellagic acid absent (C. demersum). Aluminium accumulation not found.
Geography, cytology. Temperate to tropical. Cosmopolitan. X = 12.
Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgrens Superorder Nymphaeiflorae; Nymphaeales. Cronquists Subclass Magnoliidae; Nymphaeales. APG III core angiosperms; peripheral eudicot (but not overtly assigned as such); Superorder Ceratophyllanae. APG IV Order Ceratophyllales.
Species 10. Genera 1; only genus, Ceratophyllum.
General remarks. See Les (1993), who suggested that Ceratophyllum may have arisen from angiosperms pre-dating the divergence of Monocots and Dicots. It was subsequently proposed (Chase et al., 1993) as sister to all other flowering plants, consequent on phylogenetic analyses of RuBisCO large subunit DNA sequences. It should be remembered, however, that RuBisCOs of all the submerged aquatics assayed for KmCO2 (Yeoh et al. 1981: sample including algae, bryophytes, Monocots, and both tenuinucellate and crassinucellate Dicots, but not Ceratophyllum) exhibit peculiarly high values, implying peculiar nucleotide sequences in the RuBisCO genes.
Illustrations. • Le Maout and Decaisne: Ceratophyllum. • Ceratophyllum demersum: Hutchinson. • Ceratophyllum demersum and C. submersum: Eng. Bot. 1276 and 1277, 1868. • Ceratophyllum demersum: B. Ent. 730, 1839. • Ceratophyllum: vascular anatomy of stem (Solereder, 1908).
We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG). See also Guidelines for using data taken from Web publications.
Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 5th March 2018. delta-intkey.com/angio’.