Chapter 1: The Characeae Plant

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4 very evenly arranged (Fig. 1.3d) or messy (Fig. 1.3c). Some species of Nitella can produce more than one whorl of branchlets at the nodal complexes, a condition referred to as ‘heteroclemous’ (Fig. 1.3d). Tolypella branchlets are different from those in other genera, usually with a central pluricellulate ray, secondary rays and clusters of gametangia (Fig. 1.4d). The gametangial initial cell produces the gametangia (oogonia and/or antheridia), bracteoles and sometimes a bractlet (Fig. 1.5). Oogonia have a striped appearance with a small but distinctive crown of cells (coronula) at their apex. Oogonia vary in colour from green to bright orange, and in older parts of the thallus the fertilised oospore within the oogonium becomes darker as it matures. The antheridia can also be green, but are often orange to red in colour, and in dioecious species can be so large (approaching 1 mm in diameter) as to be mistaken for ‘berries’ on the branchlets. The gametangia (oogonia and antheridia collectively) are often surrounded by bracteoles (that arise from the base of the gametangia) and bract cells (that arise from the branchlet node). These can be longer (Fig. 1.5a) or shorter than the oogonium (Fig. 1.5b). A bractlet can occur at the base of the oogonium in female dioecious plants instead of an antheridium. The distinctive characteristic of the characeae thallus is that all of the parts consist (with the exception of the gametangia and nodes) of single cells or uniseriate filaments of cells. A notable characteristic of some species of characeae is the development of a coating of calcium carbonate, ‘marl’ or ‘lime’, when growing in hard-water lakes or streams. In general, species of Lamprothamnium, Tolypella, a few species of Nitella and corticated species of Chara can develop a calcareous layer on the thallus and/or a calcified coating on the oospore (called a lime-shell or gyrogonite). However, the species that do so are not used generally in physiological studies. Calcium carbonate can be precipitated in bands on the axes and branchlets of many species of characeae as a consequence of their photosynthesis and metabolism, but this is generally distinct from the thick encrustation that occurs in calcareous habitats (see section 2.4). The growing thallus of characeae plants varies in complexity and size depending on the species. Most of the species of Chara that occur in the Northern Hemisphere (Krause 1997; Han et al 1986; Scribalo 2010) have internodes covered by a cortex of smaller, linearly aligned cells (Fig. 1.2a, b). This layer of cortical cells can prevent physical access to the
5 largest cells, and for this reason corticated species of Chara are rarely used in physiological studies (Winter et al. 1987). The rows of cortical cells are often interrupted by spine cells, which can be globular (Fig. 1.2a) or long and acute (Fig. 1.2b). They can be sufficiently abundant in some species as to make the entire thallus appear prickly. In contrast to corticated species of Chara, all members of the genera Nitella, Tolypella, Lamprothamnium and Nitellopsis and species of Chara in subgenus Charopsis are without a cortex (ecorticate), at least in part of the thallus (Fig. 1.2c). The species most commonly used in physiological studies are Chara australis, C. corallina, C. longifolia, and species of Lamprothamnium (Table 1). There are additional species that could be used in physiological studies: Chara braunii is a widespread ecorticate species (Proctor 1980), but has an annual life history, so is not commonly maintained in laboratory culture. There are also several short-range endemic species that have ecorticate stems (C. simplicissima, C. lucida in Australia, C. walichii in India), or ecorticate branchlets (C. baueri in Europe, C. curtissii in North America, C. gymnopitys and C. muelleri in Australia). A large number of Nitella species produce robust thalli with long internodes, but this genus is less commonly used in physiological studies. 1.2 Morphology of individual species There are six recognised extant (as opposed to fossil) genera in family Characeae: Chara and Nitella contain the majority of species in the family, Lamprothamnium, Nitellopsis and Tolypella have several species each, and Lychnothamnus has a single species, Ly. barbatus which is rare world-wide (Sugier et al. 2009). Many species could be useful for physiological studies, but the majority of studies are done on those species of Chara or Lamprothamnium that have already been cultured, or are common and easily introduced into culture in the laboratory (Table 1). The following list of species have been used in physiological studies and are characterises by their large cell size, lack of cortication on the axis or branchlets, relatively simple morphology and ease of collection or culture. As such, they do not represent the entire range of variation that exists in characeae plants, and have some very specialised characteristics.
Page 1 and 2: 1 Chapter 1: The Characeae Plant 1
Page 3: 3 1.1 General Morphology The chara
Page 7 and 8: 7 Lamprothamnium in 1916 to avoid
Page 9 and 10: 9 of inflated branchlets develop,
Page 11 and 12: 11 where the antheridia are termin
Page 13 and 14: 13 zygote and the maternal spiral
Page 15 and 16: 15 1.4.1 Systematics and the conce
Page 17 and 18: 17 definition of species (Proctor
Page 19 and 20: 19 bulbilifera. The natural range
Page 21 and 22: 21 do they occur?’ are central t
Page 23 and 24: 23 of animal and algal epiphytes (
Page 25 and 26: 25 1.5.4.4 Temperature Storage tem
Page 27 and 28: 27 annuals (i.e. reproducing once
Page 29 and 30: 29 growth has taken place (e.g. Ch
Page 31 and 32: 31 Figure 1.15 The characeae oospo
Page 33 and 34: 33 antheridia clustered at the bas
Page 35 and 36: 35 Casanova, M.T. and Karol, K.G.
Page 37 and 38: 37 Proctor, V.W. 1960. Dormancy an

Chapter 1: The Characeae Plant

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