Keys to Nature
A key to bryophytes - distinguishing between liverworts, hornworts, and mosses

© Matt von Konrat - Keys to Nature Project

A key to bryophytes - distinguishing between liverworts, hornworts, and mosses
Jose Gudino, Noris Salazar A. and Matt von Konrat
This is a key to a group of plants traditionally referred to as bryophytes. A broad consensus confirms that bryophytes represent three quite separate evolutionary lines, i.e., Marchantiophyta (liverworts), Anthocerotophyta (hornworts), and Bryophyta (mosses). Together, bryophytes are the second largest group of land plants after flowering plants, and are pivotal in our understanding of early land plant evolution. Bryophytes form a conspicuous feature of the vegetation in many habitats throughout the world and are of great ecological significance. This key simply serves to help in distinguishing between liverworts, mosses and hornworts. We are developing additional keys for selected taxonomic groups as well as geographical areas. Please contact the authors and if you are interested in providing feedback. We acknowledge support in part from Caterpillar Inc. and the National Science Foundation (Award No. 0949136).


Key Structure:
Draft key to bryophytes - liverworts, mosses, and hornworts

1a Plant leafy: With "leaves-on-stems" growth habit [moss or liverwort] *2*
1b Plant complex thalloid: Almost leathery, robust thallose, i.e., appearing as sheet-like green tissue [liverwort or hornwort] *2*
1c Plant simple thalloid: With "flimsy thallii, maybe superficially leaf-like [liverwort]

2a Sporophytes present (spore producing phase of the plant life cycle, often with a distinct spore-containing capsule) *3*
2b Sporophytes absent *4*

3a The sporophyte appearing as a tapering horn-like or needle-like structure. The capsule may initially be green and as spores mature it turns brown. The capsule opens by means of one or two lengthwise slits or valves. [hornwort]
3b The sporophyte with an almost translucent, often colourless stalk (or seta); the capsule splitting open into 2 or 4 valves, and never by means of a well defined mouth [liverwort]
3c Sporophyte with a green, brown or red coloured seta (in Sphagnum and Ambuchanania the seta may also be translucent); the capsule with a well-defined mouth, sometimes surrounded by peristome teeth (see below); when immature the mouth is covered by a cap called an operculum [moss]

4a Plant complex thalloid: Almost leatthery, robust thallose, i.e., appearing as sheet-like green tissue [liverwort or hornwort] *5*
4b Plant simple thalloid: With "flimsy thallii, maybe superficially leaf-like [liverwort]
4c Plant leafy: With "leaves-on-stems" growth habit [moss or liverwort] *7*

5a Surface with cup-like structures containing small vegetative (asexual) propagules or gemmae [liverwort]
5b Surface smooth, i.e., no surface structures [liverwort or hornwort] *6*

6a Thallose relatively thick, representing extensive tissue differentiation; oftens feels and appears leathery; surface usually dotted with air pores; darker spots lacking. Microscopic features: cells with many chloroplasts per cell; oil bodies present; trigones often present [liverwort]
6b Thallose relatively thin, never having the extensive tissue differentiation as in liverworts; surface without air pores; thallose appearing with darker spots scattered throughout, representing cyanobacteria. Microscopic feature: cells with only 1-2 chloroplasts per cell; oil bodies absent; trigones typically absent present [hornwort]

7a Leaves in two rows either side of stem and appearing in an almost flat plane [probably a liverwort; possibly moss] *8*
7b Leaves in a spiral arrangement [moss]

8a Individual leaf with a nerve (costa), typically showing as a distinct line along the leaf's central axis, either part way or the entire length of the leaf [moss]
8b Leaves with no nerve visible [moss or liverwort] *9*

9a Leaves lobed, divided, or with cilia (long fine points) [liverwort]
9b Leaves simple, undivided, entire or toothed margin (moss or liverwort) *10*

10a Microscopic feature: Oilbodies present (membrane-bound organelles containing secondary compounds) distinguished from green coloured chloroplasts [liverwort]
10b Microscopic feature: Oilbodies absent [probably a moss] *11*

11 Plants with multicellular rhizoids (root-like structures). Microscopic feature: Cells typically without trigones [moss]
11 Plants with unicellular rhizoids. Microscopic feature: Cells with trigones (generally triangular or circular intracellular wall thickenings, found at the point where three, or more, cells meet [liverwort]


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This page was last modified on: Tue, 5 Apr 2011 11:54:48 -0500.