CLASS CERATOPHYLLIDOPSIDA

EUKARYA> ARCHAEPLASTIDA> VIRIDIPLANTAE> STREPTOBIONTA> EMBRYOPHYTA> TRACHEOPHYTA> SPERMOPHYTA> ANGIOSPERMOPHYTA> CERATOPHYLLIDOPSIDA

Ceratophyllidopsida (se-ra-to-fi-li-DOP-si-da) is derived from the genus Ceratophyllum, which means “horn” (kerato, κέρατο) “leaf” (fyllo, φύλλο) in Greek. The suffix is comes from the Greek for “that which resembles” (opsis -οψισ). Together, they mean that which resembles Ceratophyllum. This is a class name of our creation to make it parallel in form with the other classes.

INTRODUCTION TO THE CERATOPHYLLIDOPSIDA The hornworts or coontails occupy a clade of uncertain affinities. APG I (1998) was unable to resolve the group and the family emerged among the basal angiosperms. Other molecular analyses placed them as sisters to the other angiosperms (Chase et al. 1993), sisters to the monocots (Graham and Olmstead 2000; Qiu et al. 2000), and sisters to the eudicots (Judd et al. 2002, Soltis et al. 1999, Soltis et al. 2000, APG II 2003, Hilu et al. 2003, Frohlich and Chase 2007, Graham and Iles 2009). Although APG II (2003) clearly associated the tricolpates (text with tooltip) A pollen grain with three grooves or furrows. with Ceratophyllidaceae (see Figure 1), the coontails are not tricolpates (the Eudicots or Asteropsida). To accommodate the phylogeny of APG II (2003) and APG III (2009), I have coined the class name, Ceratophyllidopsida to make it parallel to its sister group. APG II (2003) and APG (2009) have not had the last word on this group; Endress and Doyle (2009) contend that Ceratophyllum, or a plant like it, is the sister group to the Flowering Plants or among the basal families. Thus it occupies a position of Incertae Sedis and likely will find a home in the flowering plants when more is known of the phylogenetic structure of the phylum. Ceratophyllaceae is an ancient family with a fossil record to the early Cretaceous. Today, the family has a single genus (Ceratophyllum) with six species. However, the genus is almost cosmopolitan and occurs in almost all lentic aquatic systems, particularly those with hard water. The plants are aquatic herbs (Figure 2). They have no roots and the stem is reduced to an axis with a single vascular bundle (text with tooltip) One of the strands of tissue that conducts water and nutrients within the plant. Consists of xylem on the inside and phloem on the outside, separated by a layer of cambium. and a central air canal. Leaves are whorled, and often dichotomously divided (see Figure below from Gleason 1963). The plants have no stomates (text with tooltip) Pores in the leaf epidermis surrounded by a pair of guard cells. The gas exchange of leaves is controlled by the dimension of the pores. or cuticle. The axial flowers are solitary, imperfect (text with tooltip) A flower with EITHER male OR female functional reproductive structures. (monoecious), actinomorphic (text with tooltip) It is derived from two Greek roots that mean ray of light (aktina-ακτίνα) and form (morphos- μορφή). This is an adjective that defines the structure of a flower according to its symmetry. An actinomorphic flower is radially symmetrical. That is, such a flower is divisible through the center of the flower in several or many longitudinal planes such that the halves form mirror images in each case. and inconspicuous (see Figures 3 and 4). They are subtended by a whorl of seven to many bracts (text with tooltip) A reduced leaf, especially the small, scale-like leaves associated with a flower or flower cluster. (maybe modified tepals (text with tooltip) One of the petals or sepals of a flower in which the perianth segments closely resemble each other. ). The stamens (text with tooltip) One of the male sex organs, usually consisting of anther and filament. are 10 to many and distinct. Pollen (text with tooltip) The collective mass of grains produced within the anthers of flowering plants or the male cones of a gymnosperm. In all seed plants, pollen is generated by the development of a microspore into a microgametophyte. The germination of the pollen grain leads to the development of a pollen tube, which delivers two sperm or sperm nuclei to the egg in the ovule. In flowering plants, mature microgametophyte has only two cells, a tube cell and a generative cell. is without apertures, and the exine is reduced. The flower has a single hypogynous (text with tooltip) With the sepals, petals, and stamens attached to the receptacle or axis below the ovary. carpel whose stigma (text with tooltip) The apex of the style, usually enlarged, on which the pollen grains land and germinate. extends along one side of the style (text with tooltip) The elongated potion of a carpel that bears the stigma at its tip. . The fruit (text with tooltip) Mature ovary with its enclosed seeds and sometimes external structures. is an achene (text with tooltip) An achene (n) is a small, dry, 1-seeded, indehiscent fruit with a thin wall, and always derived from one carpel. It is distinguished from a nut by being thin, almost papery rather than stony. Perhaps, the most familiar achene is the fruit of the sunflower, erroneously called a sunflower seed. (see Figure 5) whose seed has no endosperm (text with tooltip) The nutritive storage tissue that grows from the fusion of a sperm cell with polar nuclei in the embryo sac. .

FIGURE 1. CLADOGRAM OF THE CERATOPHYLLIDOPSIDA WITHIN THE CONTEXT OF THE FLOWERING PLANTS. The cladistic relationships between Ceratophyllum (in green box) and other groups of flowering plants. The position of the single genus and order is consistent through almost all studies of the past 10 years (e.g. Mathews and Donoghue 2000, Soltis et al. 1999, Hilu et al. 2003, Jansen et al. 2007, APG I 1998, APG II 2003, APG III 2009, Chase and Reveal 2009).

FIGURE 2. Ceratophyllum submersum showing the whorled leaves characteristic of this group. Image by Christian Fischer and used according to the GFDL License.	FIGURE 3. Ceratophyllum demersum staminate flower as viewed with an SEM. B=bract; St=stamen. Image from Iwamoto et al. (2003).	FIGURE 4. Ceratophyllum demersum pistillate flower as viewed with an SEM. S=stem; double arrow indicates style. Image from Iwamoto et al. (2003).	FIGURE 5. Ceratophyllum demersum achene. Image from Steve Hurst of USDA and in the Public Domain.

LITERATURE CITED APG I, K. Bremer, M. W. Chase, P. F. Stevens, A. A. Anderberg, A. Backlund, B. Bremer, B. G. Briggs, P. K. Endress, M. F. Fay, P. Goldblatt, M. H. G. Gustafsson, S. B. Hoot, W. S. Judd, M. Kallersjo, E. A. Kellogg, K. A. Kron, D. H. Les, C. A. Morton, D. L. Nickrent, R. G. Olmstead, R. A. Price, C. J. Quinn, J. E. Rodman, P. J. Rudall, V. Savolainen, D. E. Soltis, P. S. Soltis, K. J. Sytsma, and M. Thulin (Angiosperm Phylogeny Group). 1998. An Ordinal Classification for the Families of Flowering Plants. Annals of the Missouri Botanical Garden. 85:531-553. [C] APG II, B. Bremer, K. Bremer, M. W. Chase, J. L. Reveal, D. E. Soltis, P. S. Soltis, P. F. Stevens, A. A. Anderberg, M. F. Fay, P. Goldblatt, W. S. Judd, M. Källersjö, J. Kårehed, K. A. Kron, J. Lundberg, D. L. Nickrent, R. G. Olmstead, B. Oxelmann, J. C. Pires, J. R. Rodman, P. J. Rudall, V. Savolainen, K. J. Sytsma, M. van der Bank, K. Wurdack, J Q.-Y. Xiang, and S. Zmartzy. 2003. The update of the angiosperm phylogeny group classification for the orders and families of flowering plants: APG II. Botanical Journal of the Linnean Society. 141:399-436. [20] APG III, B. Bremer, K. Bremer, M. W. Chase, M. F. Fay, J. L. Reveal, D. E. Soltis, P. S. Soltis, P. F. Stevens, A. A. Anderberg, M. J. Moore, R. G. Olmstead, P. J. Rudall, K. J. Sytsma, D. C. Tank, K. Wurdack, J Q.-Y. Xiang, and S. Zmartzy. 2009. An update of the angiosperm phylogeny group classification for the orders and families of flowering plants: APG III. Botanical Journal of the Linnean Society. 161: 105-121. Chase, M. W., D. E. Soltis, R. G. Olmstead, D. Morgan, D. H. Les, B. D. Mishler, M. R. Duvall, R. A. Price, H. G. Hills, Y. L. Qiu, K. A. Kron, J. H. Rettig, E. Conti, J. D. Palmer, J. R. Manhart, K. J. Sytsma, H. J. Michaels, W. J. Kress, K. G. Karol, W. D. Clark, M. Hedren, B. S. Gaut, R. K. Jansen, K. J. Kim, C. F. Wimpee, J. F. Smith, G. R. Furnier, S. H. Strauss, Q. Y. Xiang, G. M. Plunkett, P. S. Soltis, S. M. Swensen, S. E. Williams, P. A. Gadek, C. J. Quinn, L. E. Eguiarte, E. Golenberg, G. H. Learn, Jr., S. W. Graham, S. C. H. Barrett, S. Dayanandan, and V. A. Albert. 1993. Phylogenetics of seed plants: an analysis of nucleotide sequences from the plastid gene rbcL. Annals of the Missouri Botanical Garden 80:528-580. Endress, P. K. and J. A. Doyle. 2009. Reconstructing the ancestral angiosperms flower and its initial specializations. American Journal of Botany. 96(1): 22-66. Frohlich, M. W. and M. W. Chase. 2007. After a dozen years of progress the origin of angiosperms is still a great mystery. Nature. 450: 1184-1189. Graham, S. W. and W. J. D. Iles. 2009. Different gymnosperm outgroups have (mostly) congruent signal regarding the root of flowering plant phylogeny. American Journal of Botany. 96(1): 216-227. Graham, S. W. and R. G. Olmstead. 2000. Utility of 17 chloroplast genes for inferring the phylogeny of the basal angiosperms. American Journal of Botany 87:1712-1730. Hilu, K. W., T. Borsch, K. Muller, D. E. Soltis, P. A. Soltis, V. Savolainen, M. W. Chase, M. P. Powell, L. A. Alice, R. Evans, H. Sauquet, C. Neinhuis, T. A. B. Slotta, J. G. Rohwer, C. S. Campbell, and L. W. Chatrou. 2003. Angiosperm phylogeny based on MATK sequence information. American Journal of Botany. 90(12): 1758-1776. Iwamoto, A., A. Shimizu, and H. Ohba. 2003. Floral development and phyllotactic variation in Ceratophyllum demersum (Ceratophyllaceae). American Journal of Botany. 90(8): 1124-1130. Judd, W. S., C. S. Campbell, E. A. Kellogg, P. F. Stevens, and M. J. Donoghue. 2002. Plant Systematics: A Phylogenetic Approach. Second Edition. Sinauer Associates, Inc. Sunderland, MA. [L] Qiu, Y. L., J. H. Lee, F. Bernasconi-Quadroni, D. E. Soltis, P. S. Soltis, M. Zanis, E. A. Zimmer, Z. D. Chen, V. Savolainen, and M. W. Chase. 2000. Phylogeny of basal angiosperms: Analyses of five genes from three genomes. International Journal of Plant Sciences. 161:S3-S27. Soltis, D. E., P. S. Soltis, M. W. Chase, M. E. Mort, D. C. Albach, M. Zanis, V. Savolainen, W. H. Hahn, S. B. Hoot, M. F. Fay, M. Axtell, S. M. Swensen, L. M. Prince, W. J. Kress, K. C. Nixon, and J. S. Farris. 2000. Angiosperm phylogeny inferred from 18S rDNA, rbcL, and atpB sequences. Botanical Journal of the Linnean Society 133:381-461.

This name is of our invention and does not imply that the groups included are monophyletic.

By Jack R. Holt. Last revised: 03/28/2013