LOWER PLANTS 



149 



TAXONOMIC SUMMARY- 



Kingdom Plantae (Eng. plan!) — plants 

 Subkingdom Algae (L. algtic. seaweeds) — algae 

 Phv'lum Clhlorophvta (Gr. ihtoms. green + fihvtun. plant) — green algae 

 Phylum Clharophyta (Gr. (Aora. delight + phrlon) — stoneworts 

 Phvlum Ghrysophyta (Gr. chrysus. gold + phylon) — golden algae 

 Phylum Phaeophyta {Gr. photos, dusky + phylon) — brown algae 

 Phylum Rhodophyta (Gr. rhodim. red + phyUm) — red algae 



spore-forming sporangia, multicellular sex organs 

 (except in the Charophyta), embryo stages, or any 

 structure characteristic of animal organization. 



The algae probably are a natural group, all having 

 common ancestry from among the archaic chloro- 

 phyll-bearing Flagellata. In this hypothesis it is as- 

 sumed that the green algae (Chlorophyta) originated 

 from the green, or chlorophyll-bearing, Flagellata and 

 that the early green algae were ancestral to other 

 algae. Three lines of evolution are assumed from the 

 archaic green algae. In one line of development, the 

 Chlorophyta continued from their archaic ancestors 

 but also gave rise to a poorly defined phylum, the 

 Charophyta (stoneworts), and possibly to all other 

 plant phyla. In a second line, the Rhodophyta (red 

 algae) evolved. In the final line, the Ghrysophyta 

 (golden algae) and the Phaeophyta (brown algae) 

 were derived. The possibility of such a series of hap- 

 penings can be appreciated by contrasting the fea- 

 tures of the different groups of algae. 



There are other possible origins for the algae. For 

 example, each line of development, or even each phy- 

 lum, may have had independent origin from among 

 the green flagellates. Also, the Rhodophyta may 

 have had an entirely separate origin. Instead of a 

 green flagellate ancestry the red algae may have 

 evolved from the blue-green algae. 



This confusion of origin again is the consequence of 

 a poor fossil record. Although many algal fossils 

 appear to be well preserved, the remnants of these 

 simple creatures are far from being adequate. This 

 statement may be difficult to accept if one has seen 

 what appear to be excellent algal remains. However, 

 the problem is not simply one of general structure. 

 Such things as minute organization, including types 

 of pigments, chlorophyll, and food reserves, must be 

 known in order for the pattern of algal evolution to be 

 disclosed. Therefore, although the time from the first 

 conspicuous life through the Ordovician is called the 

 Age of Algae, many of the known algal fossils cannot 



be identified. However, the green algae are known 

 from the Precambrian, brown and red algae appear 

 to be represented in the Cambrian, stoneworts in the 

 Devonian, and diatoms in the Triassic. In addition, 

 in Precambrian and Cambrian deposits there are re- 

 mains of complex alga-like creatures, the very con- 

 spicuous reef-building stromatolites. As one might 

 expect, the exact nature of the stromatolites is not 

 known. They might have included remotely related 

 taxa, or they may not have been single creatures. It 

 still is suggested that they were lichen-like combina- 

 tions of red algae and blue-green algae. 



ALGAL ECOLOGY 



Algae most frequently are found in bodies of water. 

 They form the dominant flora of the ocean; few ma- 

 rine plants are not algae. About the only exception to 

 a completely algal flora in the seas is the eel grasses. 

 The eel grasses are vascular plants, or Tracheophyta, 

 that can be diagnosed by their green, reed- or grass- 

 like leaves that arise from a dark brown, under- 

 ground, slender rootstock. The rootstock is an under- 

 ground stem that bears many true roots. No marine 

 algae have such a creeping rootstock or such difTer- 

 ences in color between leaf-like and root-like struc- 

 tures. Marine algae usually are called seaweeds, and 

 the word "kelp" refers to the large, coarse marine 

 algae (mostly brown algae). 



Many other algae are found in fresh water. Most 

 of these plants create, along with certain Cyanophyta, 

 various "scums" in the water, but the Charophyta, or 

 stoneworts, form complex structures comparable to 

 those of certain marine algae — again, no true roots 

 are found. However, not all algae are aquatic or even 

 semiaquatic. Many species are found in moist or 

 semimoist terrestrial areas, for example, soil, rocks, or 

 tree trunks. As mentioned in Chapter 8, certain green 

 algae (and some blue-green algae among the Monera) 



