The group of plants popularly known as liverworts comprise the first two of the following three classes of the division Bryophyta (bryophytes):
Class I HEPATICOPSIDA (Hepaticae).
Class II ANTHOCEROTOPSIDA (Anthocerotae).
Class III BRYOPSIDA (Musci or mosses).
In New Zealand there are, on the whole, fewer liverworts than mosses, though in very wet places, such as Fiordland and the southern part of Stewart Island, liverworts may predominate, both in terrestrial and in arboreal situations. They grow luxuriantly in wet areas and, with the mosses, form a feature of the rain forest. Mosses and liverworts are botanically distinct, the liverworts having a greater variety in their vegetative organs and in the disposition of the sporophytes. As in the mosses, the life cycle of the liverworts involves a well marked alternation of generations. The gametophyte or sexual generation bears the organs of reproduction which produce the sporophyte or the asexual generation. This grows out of the gametophyte, or “plant” as we know it, and draws sustenance from it. The sporophyte in its turn develops spores which may “germinate” into a small intermediate short-lived structure called the protonema, which gives rise to the gametophyte or “plant”, and thus completes the cycle.
Hepatics are primarily divided into two groups, the leafy or foliose, and the thalloid or frondose. Owing to the phenomenon known as the alternation of generations, the liverwort “plants”, as they are usually seen and recognised, exhibit only one half of the life cycle of the organism. Briefly, the foliose hepatics are mosslike plants with a stem and leaves, and usually a third row of leaves on the under surface of the stem. The stems do not have woody fibres or vascular tissue, but there is a cortex and medulla. The variations in these and in the pattern of branching play a part in formulating genera. Unlike those of the mosses, the leaves are without a midrib and are often bilobed. The size and colour of the leafy hepatics vary considerably from minute terrestrial plants to large cushions or masses of creeping or pendulous leafy stems, in light or dark shades of green and brown or even in tones of rose.
The thalloid hepatics, less numerous than the foliose, consist of a thallus, a plant body not differentiated into stem and leaves, but flat and more or less broad. The thallus may be multi-layered, as in the order Marchantiales, or one-layered, as in Metzgeriales. “Rootlets”, called rhizoids (also common to the foliose hepatics), help to attach the thallus to the ground or substratum on which it grows.
There are at least three genera, Fossombronia, Noteroclada, and Treubia, which are intermediate between the foliose and frondose groups in that a more or less thalloid axis has lobes or leaflike appendages.
Both the leafy “plant” and the thalloid “plant” are the sexual or gametophyte generation of the life cycle. They both produce the sexual organs on some part of their surface. The female organs or archegonia are flask-shaped structures containing the embryo cell. In the leafy plants they are formed at the apex of a stem or branch-arresting growth. In the frondose group they are produced on or somewhat below the surface of the thallus, or on special combinations such as a stalked receptacle. The male organs are the spermatozoids, which are released from oval or globose, stalked or sessile bodies called antheridia. They may or may not be on the same plant as the archegonia. When the embryo cell is fertilised, the development of the second half of the life cycle, the sporophyte, at once begins. The basal part which penetrates the host to obtain nourishment is called the foot. The upper portion develops into a capsule, which produces spores internally. Protected usually by two envelopes, the inner one, the calyptra, being always present, the capsule ripens and erupts through the calyptra (this being the main difference from the mosses) to scatter the spores, either by splitting downwards into four valves or by bursting irregularly. In the foliose plants and Metzgeriales of the thalloids, the capsule usually possesses a delicate, elongate, hyaline stalk called the seta; as Hooker writes: “slender, white, cellular fruit-stalks, surmounted by 4 little brown radiating arms (valves) placed crosswise”. A variously shaped assemblage of cells, developed from the germinating spore, then gives rise to the gametophyte, and the cycle begins again.
Asexual reproduction by way of small detachable gemmae is commonly met with. It has even been suggested that, in course of time, gemmae may replace the sporophytes as a means of propagation.
Some 102 genera and 360 species have been found in New Zealand. Well-known cosmopolitan and sub-cosmopolitan genera of the leafy liverworts, such as Lophocolea, Chiloscyphus, Frullania, Radula, Plagiochila, Bazzania, Jamesoniella, Cephalozia, Acrobolbus, Isotachis, Adelanthus, and of the large family Lejeuneaceae, are well represented in New Zealand, while representatives of such northern genera as Anthelia, Marsupella, Jubula, Ptilidium, and Pedinophyllum have more recently been reported. The tropical genera, Schistochila, Acromastigum, Leptolejeunea, and Treubia, include New Zealand in their southern range, and genera exclusive or nearly so to the Southern Hemisphere, such as Marsupidium, Pachyglossa, Lepidolaena, Temnoma, Lembidium, Dendrolembidium, Balantiopsis, Triandrophyllum, and Lepicolea, are by no means lacking.
The widespread genus Lepidozia, as originally constituted, has been subdivided into at least six smaller genera of which we have Lepidozia, Telaranea, Lepidoziopsis, Microlepidozia, and Drucella. The trend is now to streamline all genera whenever possible by creating segregates that are smaller and more sharply defined. But on the other hand the unwieldy family of Lejeuneaceae is being simplified by reduction of genera.
Goebeliella is a distinguished genus, with one species not uncommon throughout New Zealand and also in the Auckland Islands; Goebelobryum, which may be endemic, revels in the peat of the Waikato.
Of the thalloid genera, New Zealand has its share. The universal Metzgeria and Riccardia, on trees and damp earth respectively, are here in plenty. The widespread Pallavicinea, the tropical and southern Symphyogyna, and the rarer southern Hymenophytum, whether dendroid or narrow fronded, alike enjoy the shade and humus of the bush. Marchantia and also Lunularia, which is possibly introduced, flourish by streams and gorges and even on shady garden paths, and the less common but more or less worldwide Reboulia, Plagiochasma, and Asterella, also with sporophyte borne on stalked receptacles, reward the searcher with their green and purple colourings; and Targionia, first noted by Linnaeus, which encloses its sporophyte in two terminal blackish scales. Wet banks clothed with the large deep-green Monoclea, known also in Chile, unfailingly attract attention, whilst Neohodgsonia, another distinctive plant, still survives in New Zealand and Tristan da Cunha.
Until recently Anthoceros and its allied genera were classed with the Hepaticae. The gametophyte is thalloid, usually dark green and multilayered, but the tissues are not differentiated. The life-history is the same as in Hepaticopsida, with the archegonia and antheridia sunk in the tissues of the thallus; the sporophyte consists of a foot, an intermediate growing region, and a long, cylindrical capsule with a central columella. The capsule, indeterminate in length, is brown or blackish and splits along the side to liberate the spores.
The New Zealand genera Anthoceros, Phaeoceros, Megaceros, and Dendroceros are found throughout the world and are reputedly difficult of determination.
As yet no handbook of the New Zealand liverworts has been compiled, but in addition to the early literature and Stephani's Species Hepaticarum there are papers in the Transactions of the Royal Society of New Zealand, and more recently R. M. Schuster has published the following important article: “Annotated Keys to the Genera of Antipodal Hepaticae with special reference to New Zealand and Tasmania”. Journal of the Haltori Botanical Laboratory, 26, 185–387 (July 1963).
by Eliza Amy Hodgson, F.L.S., F.R.S.N.Z., Amateur Botanist, Awamate R.D., Wairoa, Hawke's Bay.