We are surrounded by alien life forms.  Alien in the sense that they are foreign to us, but not alien in the sense that we don't run into them every day, for these life forms are often some of the most common.   These include mushrooms and other fungi, seaweeds, mosses, liverworts, lichens and slime  molds.  In 1703, the Swedish botanist, Carl Linaeus, introduced his Systema Natura, the first widely used system of naming and classifying things.  Linaeus knew these alien organisms well, but classified them among the sedentary plants.  Most of today's biologists have moved all, except the bryophytes, out of the plant kingdom and into other kingdoms that are only distantly related to plants.  A few, present day plant biologists talk of them as a single, polyphyletic group, lumping them into a category of plant-like organisms called "cryptogams" (literally "hidden sex cells") because they lack flowers and yet possess many of the other characteristics of plants.

     Briefly, cryptogams are defined as lower plants or plant-like organisms that reproduce by spores.  To really appreciate these organisms, it is often necessary to use a microscope, or at least, a hand lens.  Many of the features that characterize different groups or different species within groups are microscopic in size.  If you have learned of these in a biology course, or on television, likely you were just introduced without getting deeply into their interesting life histories and capabilities.  Rarely do popular presentations spend much time on these plant-like life forms, except perhaps to stress the nastiness of a few.

     Many biologists subscribe to a Six Kingdom system of high-level classification.  The following Table lists the groups commonly regarded as cryptogams (underlined) by Kingdom, along with some of the other organisms (that aren't dealt with at this site) that are classified in these Kingdoms.  Keep in mind, many intelligent people disagree about how to classify these organisms:  there is no one, correct way.
 

Kingdom	Representative groups (those underlined are cryptogams, those in bold face are treated at this site)
Kingdom Eubacteria (formerly part of Monera)	Bluegreen bacteria (free-living and one of the symbionts in some lichens)
	many other groups, at about the phylum level
Kingdom Archaebacteria (formerly part of Monera)	many groups, at about the phylum level, of unique prokaryotic organisms
Kingdom Protista ( = Protoctista of Lynn Margulis)	Green algae (free-living and one of the symbionts in some lichens)
	many other algae in other phyla (including the seaweeds)
	protozoa
	Slime molds
Kingdom Mycota (=Fungi)	Basidiomycota (mushrooms and relatives)
	Ascomycota (cup fungi and relatives)
	Lichens (the fungal symbionts in lichens are mostly Ascomycetes; a few are Basidiomycota)
	Molds (simple fungi without "fruit bodies")
	Yeasts (simple fungi adapted to living as single cells in liquids)
Kingdom Plantae	Bryophytes (mosses, liverworts and hornworts)
	Vascular cryptogams (ferns, horsetails & club mosses)
	Higher vascular plants (conifers, flowering plants)
Kingdom Animalia -- non of these are regarded as cryptogams	Various invertebrate animal phyla
	Vertebrate animals (in the phylum Chordata)

     There are many good resources for all these organisms on the Internet.  Rather than list all of them, the following sites are good, relatively stabile, starting points that will point to many other quality sites.  These were all last tested as viable in early 2007.

Fungi (Basidiomycetes, Ascomycetes and lower fungi)
     Taylor Lockwood's beautiful mushroom photos
     Tom Volk's fungi pages

Lichens
     Lichenland in Oregon
     USFS Air biomonitoring program using lichens
     North American Lichen Project

Slime molds
     Myxomycete Web

Algae (including bluegreen bacteria)
     Smithsonian algae links page

Bryophytes
     Southern Illinois University Bryophyte Introduction

General
     The Microbial World
     Scott Russell's Botanical Links
     Naturalist Perspective