THE NONVASCULAR EMBRYOPHYTES

EUKARYA> ARCHAEPLASTIDA> VIRIDIPLANTAE> STREPTOBIONTA> EMBRYOPHYTA> BRYOPHYTES

INTRODUCTION TO THE NONVASCULAR EMBRYOPHYTES These are nonvascular archegoniate plants (embryophytes) that seem to be related; however, as illustrated by Tudge (2000), they do not form a natural group. The liverworts and hornworts are sister groups, but the mosses are sisters to the vascular plants. Besides the absence of vascular tissue (though some hepatophytes and mosses do have conductive tissue), they all have a dominant gametophyte stage and a more reduced or ephemeral sporophyte. In the hepatophytes and mosses the sporophyte is determinate and parasitic on the gametophyte. Kenrick and Crane (1997) report that membrane-bound tetrads of spores, signature structures of embryophytes, have been found in the mid Ordovician Period (see the Geological Time Scale). These likely were liverwort-like plants and as such did not leave any recognizable megafossils. Early Silurian fossils of individual spores are interpreted as the appearance of mosses and hornworts, organisms that have adaptations for shedding spores over extended periods. The transition from this “Eoembryophytic” (Kenrick and Crane 1997) flora to the vascular land plants occurred by the mid Silurian when unmistakable megafossils of plants bearing xylem (text with tooltip) Xylem is vascular tissue that conducts water and functions when the cells are dead. Cell types include tracheids, xylem fibers, and vessels. appeared

FIGURE 1. MAJOR CLADES OF THE NON- VASCULAR EMBRYPOHYTES. This figure is adapted from Bold et al. (1987) and Kenrick and Crane (1997).

This diagram shows the relationships as proposed by Kenrick and Crane (1997). 1. Clade 1 includes all of the Embryophytes; plants whose gametophytes produce antheridia (text with tooltip) Male reproductive structure that produces and protects sperm in embryophytes. and archaegonia (text with tooltip) The female reproductive organ containing the egg. . 2. The Hepatophytes (Liverworts) have a photosynthetic gametophyte of varying complexity and a sporophyte that is quite simple with a foot (text with tooltip) The region of the sporophyte that is anchored within the gametophyte. , seta (text with tooltip) The stalk of the sporophyte capsule. , and capsule (text with tooltip) The sporangium of the sporophyte; elevated by the seta. that may or may not have lines of dehiscence. Also, the sporophytes have little sterile tissue. 3. Plants with more complex sporophytes, usually with much sterile tissue and often with photosynthetic tissue. 4. The Hornworts produce sporangia that emerge by indeterminate growth (text with tooltip) Having the capacity for continuous growth at the apex. and have much sterile tissue, some of which is photosynthetic. 5. The Moss + Vascular Cryptogam clade makes plants with increasingly complex sporophytes. 6. The Mosses make very complex gametophytes (text with tooltip) Also called the Gametangiophore; A modified branch bearing the gametangia. , usually with upright leafy gametophores. Sporophytes are determinate and complex with a large amount of sterile tissue.

GENERAL CHARACTERS OF THE NON-VASCULAR EMBRYOPHYTE PHYLA. Information taken from Bold et al. (1987), Schofield (1985), and Margulis and Schwartz (1998).
Characters	Marchantiophyta	Anthocerotophyta	Bryophyta
form of gametophyte	thalloid to leafy	thalloid	leafy
chloroplasts	many small chloroplasts per cell; confined to gametophyte	one large chloroplast per cell; with pyrenoids; found in sporophytes and gametophytes	many small chloroplasts per cell; usually confined to gametophyte but present in some cells of the sporophyte
gametophores	gametophores absent to well-developed	no gametophores	gametophores dominant form
sporophyte	determinate; usually with simple capsules containing little sterile tissue; no elaters	indeterminate with intercalary growth; capsule complex with much sterile tissue and photosynthetic; with elaters	determinate; capsules complex with much sterile tissue and usually with distinctive peristomal structures

LITERATURE CITED Bold, H. C., C. J. Alexopoulos, and T. Delevoryas. 1987. Morphology of Plants and Fungi. 5th Edition. HarperCollins Publishers, Inc. New York. Kenrick, P. and P. R. Crane. 1997a. The origin and early evolution of plants on land. Nature. 389:33-39. Margulis, L. and K. Schwartz. 1998. Five kingdoms, an illustrated guide to the phyla of life on earth. 3rd Edition. W. H. Freeman and Company. New York. Pearson, L. C. 1995. The Diversity and Evolution of Plants. CRC Press. New York. Schofield, W. B. 1985. Introduction to Bryology. Macmillan Publishing Co. New York. Tudge, C. 2000. The Variety of Life, A Survey and a Celebration of all the Creatures That Have Ever Lived. Oxford University Press. New York.

By Jack R. Holt. Last revised: 03/26/2013