Monoecious or dioecious annual or perennial herbs, often fleshy and bristly, usually with tendrils. Leaves alternate. Flowers unisexual, racemose, clustered or solitary. Calyx normally 5-lobed; rarely sepals free. Corolla normally 5-lobed, yellow or white. Stamens 5, often reduced to 3, two double and one single; anthers twisted or contorted. Ovary inferior; carpels united, usually 1–3 celled; placentation parietal. Stigmas as many as carpels. Fruit normally a fleshy, indehiscent berry, sometimes of considerable size; seeds usually numerous.

Contains about 120 genera and 800 species, cosmopolitan but mainly in tropical and warm temperate areas.

Much of what is in this flora is owed to the great historic background to plant taxonomy here in Cambridge. One cannot but feel that one is following in a great tradition when studying the British and Irish floras in the Cambridge University Herbarium, its Library and the University Botanic Garden and when using them to work out the results of one's fieldwork.

When the modern western world took shape after the so-called Dark Ages it was France, Germany, Italy and the Low Countries that produced the pioneers of the science of botany. The medievalists were remote from any scientific appreciation of nature. An example of the work of a Cambridge scholar towards the end of that period is the book by John Maplet, A greene forest, or A naturall historie vvherein may bee seene first the most sufferaigne vertues in all the whole kinde of stones & mettals: next of plants, as of herbes, trees, shrubs, lastly of brute beastes, foules, fishes, creeping wormes serpents, published in 1567. It would be thought that by then the Renaissance and Reformation would have been established, but in thought this book is purely medieval. The breakdown of medieval ideas in England was to start at Oxford and then to be transferred to Cambridge, and it was the spirit of Erasmus in his writings, and above all in his edition of the New Testament, that gave an impetus to Greek studies and a new understanding of classical civilisation in the University.

Two men at Cambridge, William Turner and John Caius, can properly be said to have started the long line of field naturalists in Britain. Both studied in Italy and both were friends of the great Zurich naturalist Conrad Gesner. Of the two, William Turner was by far the more important botanically, being one of the most vigorous of reformers and our first scientific student of botany and zoology.

William Turner (1508–1568) was born at Morpeth in Northumberland and as a boy was said to notice the ways of animals and plants. In 1526 he went up to Pembroke Hall in Cambridge, where he stayed until 1537 and published a number of works. His teachings as a reformer got him into trouble and he went abroad, whether by order or his own choice is not known. He visited Belgium, Holland, Germany, Italy and Switzerland.

Aquatic or terrestrial, perennial, heterosporous herbs. Stems 1, rarely 2 rings of meristematic cells producing secondary tissue, short and stout, dichotomously branched, the roots arising from the 2- or 3-lobed stem base. Leaves crowded in a dense rosette, subulate or filiform, usually more or less terete, often tubular and septate, sheathing at base; with a minute ligule on the upper side near the base. The first-produced leaves in any season bearing megasporangia, the next microsporangia, and the last sterile. Sporangia sessile, more or less embedded in the leafbase below the ligule and usually covered by an indusium formed from the leaf-base. Spores on germination giving rise to prothalli. Male gametophytes (from microspore) of one vegetative cell and an antheridium, with a 4-celled wall surrounding 2 cells which give rise to 4 spermatozoids. The multiciliate spermatozoids are liberated by the dehiscence of the spore and breaking down of the antheridium wall. Female gametophyte (from megaspore) is manycelled, fills the megaspore and bears archegonia, the necks of which protrude from the split top of the megaspore. The young plant develops with a resting stage from the fertilised archegonium.

Contains 2 genera, Isoetes and the monotypic Stylites from the Andes of Peru, sometimes only recognised as a subgenus.

Perennial herbs, often with woody bases, or small shrubs. Leaves opposite, without stipules, often ericoid. Flowers solitary, terminal or in the forks of the branchlets. Calyx somewhat fleshy; lobes 5, connate at base. Petals 4–6, clawed, with a scale-like appendage on the claw. Stamens usually 6, in 2 whorls of 3; anthers 2-celled, opening lengthwise. Style 1, divided into 3 near the apex; stigmas 3, elongate. Ovary superior, 1-celled, with 2–4 parietal placentae; ovules numerous. Fruit a capsule enclosed in the calyx, opening by valves; seeds endospermous; embryo straight and axile.

Frankenia L.

As family.

Contains about 80 species with the distribution of the family.

Annuals or slightly to moderately woody perennials. Leaves opposite and often decussate or alternate, simple, usually entire, usually thick and succulent; petiole present or absent; stipules absent. Flowers solitary or in cymes, actinomorphic, usually bisexual, epigynous to perigynous. Hypanthium usually cup-shaped and persistent, often regarded as the tube of the calyx. Sepals 4–5(–6), joined to the rim of the hypanthium. Petals, actually petaloid staminodes, absent or numerous and more or less free and in one to several rows, usually linear and often brightly coloured. Stamens 3 to numerous, usually in several rows. Styles as many as carpels, free or fused at the base; stigmas minute or linear. Fruit a hooded, dehiscent or indehiscent capsule with 3 to many seeds or succulent with many seeds; loculi often roofed.

About 130 genera with some 2500 species, widely distributed but common in South Africa.

These organisms are important members of the plankton in both fresh and marine waters, although a much greater variety of forms is found in marine members. Generally the Dinophyceae are less important in the colder polar waters than in warmer waters. The highly elaborate Dinophysales (Fig. 7.47(d), (e)) are essentially a tropical group.

A typical motile dinoflagellate (Figs. 7.1, 7.2) consists of an epicone and hypocone divided by the transverse girdle or cingulum. The epicone and hypocone are normally divided into a number of thecal plates, the exact number and arrangement of which are characteristic of the particular genus (Figs. 7.1, 7.3, 7.20(b), 7.24(b)). There is a longitudinal sulcus running perpendicular to the girdle. The longitudinal and transverse flagella emerge through the thecal plates in the area where the girdle and sulcus meet. The longitudinal flagellum projects out from the cell, whereas the transverse flagellum is wave-like and is closely appressed to the girdle. The cells can be photosynthetic or colorless and heterotrophic. Photosynthetic organisms have chloroplasts surrounded by one membrane of chloroplast E.R., which is not continuous with the outer membrane of the nuclear envelope. Chlorophylls a and c 2 are present in the chloroplasts, with peridinin and neoperidinin being the main carotenoids. About half the Dinophyceae that have been examined by electron microscopy have pyrenoids in the chloroplasts (Dodge and Crawford, 1970). The storage product is starch, similar to the starch of higher plants (Vogel and Meeuse, 1968), which is found in the cytoplasm. An eyespot may be present. The nucleus has permanently condensed chromosomes and is called a dinokaryotic or mesokaryotic nucleus.

Cell Structure

Theca

The thecal structure of motile Dinophyceae consists of an outer plasmalemma beneath which lies a single layer of flattened vesicles (Figs. 7.2, 7.3(c), 7.5) (Dodge and Crawford, 1970 ; Sekida et al., 2004). These vesicles, which normally contain cellulosic plates, give the theca its characteristic structure. The actual form and arrangement of the thecal plates varies from none in the phagotrophic Oxyrrhis marina, to very thick plates with flanges at the edges in Ceratium (Figs. 7.11, 7.48, 7.49) and Peridinium spp. (Figs. 7.2, 7.10).

It was that eccentric British soldier of fortune Col. Meinertzhagen, in his Birds of Arabia, who expressed the sentiment that prefaces should be kept short because few people ever read them. Accordingly, I would like to take a brief opportunity to express my gratitude to the people who offered encouragement and assistance during the preparation of this book. I would like to thank Adele Strauss Wolbarst, Robert Cnoops, Charmaine Slack, Sophia Skiordis, Caroline Mondel, Jill Keetley- Smith, Heather Edwards, Gail Arbeter, and the Lending Library at Boston Spa, England, for help while most of this manuscript was being prepared at the University of the Witwatersrand. For general encouragement while at Pahlavi (Shiraz) University and for providing assistance during the last turbulent and chaotic year of imperial rule in Iran, while the manuscript was being finished, I would like to thank Mark Gettner, Brian Coad, and Mumtaz Bokhari. When photographs or drawings have been taken directly from the original material, this is indicated by stating in the legend that it is from the original work. Most of the drawings have been redrawn to suit my tastes, and these drawings are indicated by stating that the work is after the original.

In some cases I have made drawings from photographs or have incorporated a number of drawings in one, in which case I state that the finished drawing is adapted from the original work or works. I have used the metric system in this book, and the fine-structural illustrations are expressed in micrometers (μm) and nanometers (nm).

Eustimatophytes are yellow-green unicells that occur in freshwater, brackish water, and seawater as well as in the soil. The cells are similar to those in the Xanthophyceae, but differ in having an eyespot outside the chloroplast (Fig. 12.1) (the eyespot in the Xanthophyceae is in the chloroplast) (Hibberd and Leedale, 1970). Other characteristics of the class include a basal swelling of the tinsel flagellum adjacent to the eyespot, only chlorophyll a, chloroplasts without girdle lamellae and no peripheral ring of DNA, and chloroplast endoplasmic reticulum not connected to the nuclear envelope (Schnepf et al., 1996).

The eyespot (Figs. 12.1, 12.2) is a large orangered body at the anterior of the motile cell and is completely independent of the chloroplast. It consists of an irregular group of droplets with no membrane around the whole complex of droplets. The flagellar sheath is extended to form a T-shaped flagellar swelling at the base of the tinsel flagellum (Figs. 12.1, 12.2). This swelling is always closely appressed to the plasmalemma in the region of the eyespot. In turn, in the eyespot there is a large droplet closely applied to the plasmalemma in the area of the flagellar swelling.

The chloroplasts of the Eustigmatophyceae have chlorophyll a and β-carotene, with the two major xanthophylls being violaxanthin and vaucheriaxanthin (Whittle and Casselton, 1969 ; Antia and Cheng, 1982), the only difference in pigments compared to the Xanthophyceae being the presence of violaxanthin and the absence of antheraxanthin. Violaxanthin is the major lightharvesting pigment in the Eustigmatophyceae (Owens et al., 1987).

The Eustigmatophyceae is a monophyletic group (Andersen et al., 1998). Most of the species produce zoospores with only a single emergent flagellum (Pleurochloris magna, Fig. 12.1(d) ; Polyhedriella helvetica, Fig. 12.1(b))(Hibberd and Leedale, 1972), but there is a second basal body present, indicating that the cells had a biflagellate ancestor. The emergent flagellum is tinsel with microtubular hairs, and the flagellum is inserted subapically. Two of the algae in the class, Ellipsoidion acuminatum and Pseudocharaciopsis texensis (Fig. 12.2) (Lee and Bold, 1973), have zoospores with a long forward tinsel flagellum and a short posteriorly directed smooth flagellum.

It is possible to write whole books on the relationships between algae and the environment. In this chapter I have chosen a few subjects that have generated the most interest in the past couple of decades.

Toxic Algae

Algae can be harmful in two basic ways (Hallegraeff et al., 2003 ; Lassus et al., 2016).

The Rhodophyta (red algae) and Chlorophyta (green algae) form a natural group of algae in that they have chloroplasts surrounded by only the two membranes of the chloroplast envelope. The endosymbiotic theory of chloroplast evolution, first proposed by Mereschkowsky in 1905, is the one most widely accepted for the evolution of the chloroplast (Fig. III.1). According to this theory, a cyanobacterium was taken up by a phagocytic organism into a food vesicle. Normally the cyanobacterium would be digested by the flagellate, but by chance a mutation occurred, with the flagellate being unable to digest the cyanobacterium. This was probably a beneficial mutation because the cyanobacterium, by virtue of its lack of feedback inhibition, secreted considerable amounts of metabolites to the host flagellate. The flagellate in turn gave the cyanobacterium a protected environment, and the composite organism was probably able to live in an ecological niche where there were no photosynthetic organisms (i.e., a slightly acid body of water where free-living cyanobacteria do not grow; see Chapter 2). Pascher (1914) coined terms for this association; he called the endosymbiotic cyanobacteria cyanelles; the host, a cyanome; and the association between the two, a syncyanosis. In the original syncyanosis, the cyanelle had a wall around it. Because the wall slowed the transfer of compounds from the cyanelle to the host and vice versa, any mutation that resulted in a loss of wall would have been beneficial and selected for in evolution. As evolution progressed, these two membranes became the chloroplast envelope, the cyanome cytoplasm took over the formation of the storage product and the polyhedral bodies containing ribulose-1,5-bisphosphate carboxylase/oxygenase differentiated into the pyrenoid.

Most of the genes from the endosymbiotic cyanobacterium were transferred to the host nucleus while a small number of these genes were maintained in the resulting plastid and gave rise to the plastid genome with its associated proteinsynthesizing system. The products of many of the cyanobacterial genes transferred to the nucleus were then retargeted to the plastid to keep it functional. Approximately 3000 nuclear genes in plants encode plastid proteins, whereas the chloroplast genome contains between 100 and 120 genes. The nucleus is also capable of sensing the state of the chloroplast and to react to maintain chloroplast homeostasis.

Algae with two membranes of chloroplast endoplasmic reticulum (chloroplast E.R.) have the inner membrane of chloroplast E.R. surrounding the chloroplast envelope. The outer membrane of chloroplast E.R. is continuous with the outer membrane of the nuclear envelope and has ribosomes on the outer surface (Fig. V.1).

The algae with two membranes of chloroplast E.R. evolved by a secondary endosymbiosis (Fig. V.1) (Lee, 1977 ; Keeling, 2013) when a phagocytic protozoan took up a eukaryotic photosynthetic alga into a food vesicle. Instead of being phagocytosed by the protozoan, the photosynthetic alga became established as an endosymbiont within the food vesicle of the protozoan. The endosymbiotic photosynthetic alga benefited from the acidic environment in the food vesicle that kept much of the inorganic carbon in the form of carbon dioxide, the form needed by ribulose bisphosphate/carboxylase for carbon fixation (see Part IV for further explanation). The host benefited by receiving some of the photosynthate from the endosymbiotic alga. The food vesicle membrane eventually fused with the endoplasmic reticulum of the host protozoan, resulting in ribosomes on the outer surface of this membrane, which became the outer membrane of the chloroplast E.R. Through evolution, ATP production and other functions of the endosymbiont's mitochondrion were taken over by the mitochondria of the protozoan host, and the mitochondria of the endosymbiont were lost. The resulting cytology is characteristic of the extant algae in the Chlorarachniophyta and Cryptophyta, which have a nucleomorph representing the degraded endosymbiotic nucleus, as well as storage product produced in what remains of the endosymbiont cytoplasm.

The type of chloroplast E.R. that exists in the Heterokontophyta and the Prymnesiophyta resulted from further reduction. The nucleomorph was completely lost and storage product formation was taken over by the host. The resulting cell had two membranes of chloroplast envelope surrounding the chloroplast. Outside of this was the inner membrane of chloroplast E.R. that was the remains of the plasma membrane of the endosymbiont. Outside of this was the outer membrane of chloroplast E.R. which was the remains of the food vesicle membrane of the host. Most of the protein synthesis of the endosymbiont was taken over by the nucleus of the host (Martin, 2010).

The Synurophyceae are closely related to the Chrysophyceae (Ariztia et al., 1991). The Synurophyceae differ, however, from the Chrysophyceae in the following: the Synurophyceae have chlorophylls a and c 1 (Andersen and Mulkey, 1983), the flagella are inserted into the cell approximately parallel to one another (Fig. 11.1), there is a photoreceptor near the base of each flagellum, there is no eyespot, and the contractile vacuole is in the posterior portion of the cell (Lavau et al., 1997 ; Andersen et al., 1999). Chloroplast endoplasmic reticulum is present in a few species, but absent in most. The cells usually are covered by bilaterally symmetrical scales.

In the Synurophyceae, scales composed of silica commonly occur outside the cell (Figs. 11.1, 11.2, 11.3). The scales are bilaterally symmetrical and are formed in a silica deposition vesicle. The membrane of the silica deposition vesicle (the silicalemma) controls the shape of the scale along with proteins and glycoproteins that adhere the developing scale to the silicalemma (Schultz et al., 2001). The presence of germanium in the medium results in inhibition of scale formation (Klaveness and Guillard, 1975). The scales are carried in the scale vesicle to the plasma membrane where the plasma membrane and the scale vesicle fuse, releasing the scales outside the cell (Beech et al., 1990). The scales are held next to the cell in an organic envelope (Ludwig et al., 1996), which is either hyaline or yellow-brown, the latter appearance being due to the impregnation of iron salts. The scales of the Synurophyceae are commonly composed of a number of parts, such as the dome, shield, and bristle of Mallomonas (Lavau and Wetherbee, 1994) (Figs. 11.2, 11.3(c), (d)). The scales of the Synurophyceae are overlapped precisely so that the anterior end of one scale overlaps the right margin of the scale to its left (Leadbeater, 1990). The scales are cemented together to form a scale case by the organic envelope. This precise arrangement of scales differs from the loosely arranged scales of the Chrysophyceae.

Analysis of lake sediments often reveals the presence of the silicified scales of the Synurophyceae as well as the silicified frustules of diatoms (Smol et al., 1984 ; Dixit et al., 1999).