American Journal of Botany 91 10 1508 1522 2004 BIOLOGY AND SYSTEMATICS OF HETEROKONT AND HAPTOPHYTE ALGAE1 ROBERT A ANDERSEN Bigelow Laboratory for Ocean Sciences P O Box 475 West Boothbay Harbor Maine 04575 USA In this paper I review what is currently known of phylogenetic relationships of heterokont and haptophyte algae Heterokont algae are a monophyletic group that is classified into 17 classes and represents a diverse group of marine freshwater and terrestrial algae Classes are distinguished by morphology chloroplast pigments ultrastructural features and gene sequence data Electron microscopy and molecular biology have contributed significantly to our understanding of their evolutionary relationships but even today class relationships are poorly understood Haptophyte algae are a second monophyletic group that consists of two classes of predominately marine phytoplankton The closest relatives of the haptophytes are currently unknown but recent evidence indicates they may be part of a large assemblage chromalveolates that includes heterokont algae and other stramenopiles alveolates and cryptophytes Heterokont and haptophyte algae are important primary producers in aquatic habitats and they are probably the primary carbon source for petroleum products crude oil natural gas Key words chromalveolate chromist chromophyte flagella phylogeny stramenopile tree of life Heterokont algae are a monophyletic group that includes all photosynthetic organisms with tripartite tubular hairs on the mature flagellum discussed later also see Wetherbee et al 1988 for definitions of mature and immature flagella as well as some nonphotosynthetic relatives and some that have secondarily reduced or lost tripartite hairs Brown seaweeds diatoms and chrysophytes are commonly known members of the group Haptophyte algae are a monophyletic group that includes all photosynthetic organisms with a haptonema as well as some nonphotosynthetic relatives and some that have secondarily lost the haptonema The haptonema from which the group derives its name is a microtubule supported appendage that lies between two approximately equal flagella for review Inouye and Kawachi 1994 The coccolithophores and genera such as Pavlova and Isochrysis are commonly known members of the group Representatives of heterokont algae and haptophytes are shown in Figs 1 24 Until 1992 haptophytes were included or closely aligned with heterokont algae but a nuclear small subunit ribosomal RNA SSU rRNA analysis indicated they are distantly related Bhattacharya et al 1992 Recent molecular studies based on other genes have now indicated that heterokont and haptophyte algae may be more closely aligned than the SSU rRNA data indicated Yoon et al 2000a b Harper and Keeling 2003 Ryall et al 2003 Historical perspective Brown seaweeds were referred to in early Chinese ca 3000 BC Greek e g Theophrastos ca 300 BC and Japanese ca 500 AD writings and knowledge of brown seaweeds likely predated recorded history In early human history brown seaweeds were used for human and animal food medicinal purposes and dyes Most other heterokont algae are microscopic although mats of macroscopic Vaucheria Xanthophyceae may have been known but not recorded in historical works The first modern scientific report is the description of Fucus Manuscript received 31 December 2003 revision accepted 22 June 2004 I thank David Patterson and Hiroshi Kawai for providing color photographs of algae and Stacy Edgar for assistance with phylogenetic analysis Supported by NSF grants DEB 0206590 and DEB 0212138 E mail randersen bigelow org 1 Phaeophyceae by Linnaeus 1753 and shortly thereafter microscopic chrysophytes currently 5 Oikomonas Anthophysa were described by Mu ller 1773 1786 The history of heterokont algae was recently discussed in detail Andersen 2004 and four distinct periods were identified The discovery period 1753 1882 is that era in which brown algae were described as plants and microalgae were described as infusoria and treated as animals Perhaps the most significant publication of the era was the two part publication of Ehrenberg 1838 that contained his light microscopic observations The first synthesis period 1882 1914 began when brown algae and microalgae were first integrated and phylogenetic relationships were discussed Rostafinski 1882 Correns 1892 Klebs 1893a b Lemmermann 1899 Blackman 1900 but the period ended when these two groups were once again separated Pascher 1914 The floristic period 1914 1950 was dominated by the description of many species There was a nearly complete absence of evolutionary discussion for the primary reason that the light microscope was unable to resolve characters for determining relationships Fritsch 1935 The second synthesis period 1950 2002 began with and was dominated by evolutionary and phylogenetic relationships e g Chadefaud 1950 Bourrelly 1957 Taylor 1976 Leipe et al 1996 Daugbjerg and Andersen 1997a b Transmission electron microscopy provided a wealth of new and phylogenetically informative data e g Dodge 1973 Hibberd 1976 Taylor 1976 Andersen 1987 and biochemical studies were also initiated e g Strain 1951 Quillet 1955 Archibald et al 1963 Ragan and Chapman 1978 Smestad Paulsen and Myklestad 1978 Bj rnland and Liaaen Jensen 1989 Jeffrey 1989 Cladistic analysis brought new ways for analyzing evolutionary relationships e g Hibberd 1979 Lipscomb 1989 Andersen 1991 Williams 1991 Sorhannus 2001 and molecular systematics added powerful new data sets e g Gundersen et al 1987 Leipe et al 1994 1996 Guillou et al 1999b Moriya et al 2002 Goertzen and Theriot 2003 Discoveries led to descriptions of many new taxa including several classes Eustigmatophyceae Hibberd and Leedale 1970 Dictyochophyceae Silva 1980 Synurophyceae Andersen 1987 Coscinodiscophyceae and Fragilariophyceae Round et al 1990 Chrysomerophyceae Cavalier Smith et al 1995 1508 October 2004 ANDERSEN HETEROKONT Bolidophyceae Guillou et al 1999a Pelagophyceae Andersen et al 1993 Phaeothamniophyceae Bailey et al 1998 Pinguiophyceae Kawachi et al 2002b and Schizocladiophyceae Kawai et al 2003 The sequencing of the Thalassiosira pseudonana genome initiated in 2002 was thought to be the start of a new period but it is too early to define this period The first record of haptophyte algae might begin with Ehrenberg 1836 who discovered that chalk was composed of tiny crystallites that he considered to be formed by precipitation rather than biological activity see Green and Jordan
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