Marchasta areolata, Campbell, a New Monotypic Genus of the Marchantiaceae
[Read before the Wellington Branch, December 17, 1958; received by Editor, December 18, 1953]
A new monotypic genus of the Marchantiaceae is described and illustrated.
Description of Marchasta, Campbell gen. n.
Monoica; thallus scyphuliferus; costa humilis, crassa; alae cavernosae. Androecia disciformia, pedunculata, terminales. Carpocephala pedunculata, terminales; capitula semicircula, profunde quadrifissa, segmentis bilobatis. Involucra cylindrica, inflata, ore angustato bilabiato. Perianthia hyalina. Capsula globosa, paulum exserta, ad basin regulariter 4 vel 5 valvis late expansis dehiscens, pariete unistrata semiannulatim vel annulatim incrassata. Elatera longe attenuata, bispira. Sporae 1-cellulares, alatae.
The plant is monoecious. The thallus has cupules containing gemmae, a shallow compact midrib and wings full of air chambers. The stalked antheridiophores are disc-shaped and borne terminally on the thallus. The carpocephala are likewise terminal and stalked, with semi-circular heads deeply cleft into 4 parts which in turn are bilobed. The involucre is cylindrical and inflated with a narrow two-lipped opening A colourless pseudoperianth is present. The spherical capsule projects slightly and opens into 4 or 5 valves which spread out into a star shape. The jacket of the capsule is one cell thick and is strengthened by rings or half-rings on the walls of the cells. The elaters are long-tapering with two spirals of thickening. The spores are unicellular and winged.
The type of the new genus Marchasta, Camp. is Marchasta areolata, Camp. sp.n. described below.
Description of Marchasta areolata, Campbell gen.n., sp.n.
Planta thallosa, tenuis, spongiosa, scyphulifera, viridis subviridibus maculis, terricola, arcte repens. Thallus ad 40 mm. longus, ad 8 mm. latus, furcatus, ex apice vel ex latere costae innovatus, lobis obovatis, apice breviter incisis, late expansis, margine leviter undulatis. Alae cavernosae; cavernae amplae, liberis filis parvis raris; cellulae epidermidis incrassatae. Costa postice plano-convexa, crassa, rhizoidibus dimorphis et tenuissimis squamis vestita, sensim in alas attenuata: stratum anticum duplo altum costae, cavernosum. Stomata composita, antice conico prominula, poro magno aperto, postice conico-cylindrica, in lumen cavernarum pendula, poro interno subquadrato, 4 cellulis circumdato. Squamae juventute pellucidae, triangulatae, margine clavatas muciferes cellulas ferentes, aetate fuscae. Scyphuli margine denticulati, dentibus triangulatis, acuminatis, pellucidis, 5–7 cellulas longis; gemmae uno solo apice.
Inflorescentia monoica. Androecia disciformia, pedunculata, pedunculus terminalis, ex apice costae ortus, ad 8 mm. longus. Antheridia numerosa, ovata, breviter pedicellata, alveolis monandris, ore parvo conico-prominulo.
Carpocephala pedunculata; pedunculus terminalis, ex apice costae ortus, ad 20 mm. longus, apice paucis acuminatis squamis barbatus. Capitula semicircula, profunde quadrifissa, interdum octofissa, segmentis bilobatis, lobis leniter decurvis, postice subcarinatis. Involucra ex margine loborum orta, basi longe coalita, ad extere bilabiata, labiis primo clausis deinde hiatu angusto separatis. Perianthia monogyna, ovata, hyalina. Calyptra evanida. Capsula globosa, brunnea, matura paulum exserta, ad basin regulariter 4 vel 5 valvis late expansis dehiscens, pariete unistrata semiannulatim vel annulatim incrassata. Elatera 240–625μ longa, medio 9μ lata, longe attenuata, bispira. Sporae diametro 18–25μ, 1-cellulares, ala lata, siccitate rugosa.
The above description is based on material collected by the writer in Weinmannia-Metrosideros forest at 300 m. altitude at Waiho, South Westland, on November 24, 1942, and on October 9, 1953. The type specimen (n.531) was collected beside the track to Alec's Knob on October 9, 1953, and is lodged in the herbarium at Massey Agricultural College, Palmerston North.
In favourable situations Marchasta areolata occurs as a clan (Tansley and Chipp, 1926, p. 18) spread in irregular fashion over an area of a square metre. The substratum is always well-drained and consists of leaf litter which has accumulated amongst the exposed roots of fallen trees or in similar locations.
The thallus is slender, up to 40 mm. long and up to 8 mm. broad. It grows horizontally over the ground and branches dichotomously (Fig. 1). The lobes are
Fig. 2.—Habit drawing of a part of the thallus with an anthenidiophore and a carpocephalum. a, adventitious branch. × 2
obovate, incised at the tip, broadly spreading and with a slightly wavy margin. The whole plant is of a very characteristic and striking appearance with flecks of pale green on a background of deeper green. This appearance is due to the fact that the dorsal surface is marked into polygonal areas, each with an air pore at its central point. The pale green areas represent air chambers and the deeper green network represents the vertical partitions between the air chambers. On the ventral surface there is a midrib region where there occur rhizoids of two types and also delicate scales, which at first are colourless but later turn brown. The ventral surface of the wings shows dark green lines radiating outwards from the midrib and connecting with each other near the margin of the thallus, leaving between them pale green bands which represent large air chambers.
Vegetative multiplication takes place freely in a number of ways. It occurs as a result of the progressive decay of the older portions of the thallus. It occurs under humid conditions when adventitious shoots (Fig. 2) develop freely on the ventral surface near the tip and at the sides of the midrib; these are readily detached as their connection to the main portion of the thallus is extremely slender. A third method of vegetative multiplication is by gemmae. These develop in the cup-shaped cupules which occur on the dorsal surface of some of the branches (Fig. 1). The gemmae, when mature, float off in water and develop into new plants.
Vegetative growth of the thallus is terminated by the formation of an antheridiophore or of a carpocephalum at the apical notch (Fig. 1). As a rule both occur on the one thallus. although it is possible to find thalli showing only one type.
The antheridiophore has a stalk up to 8 mm. in height and a disc-shaped head. The antheridia are sunk in flask-shaped cavities which open on the dorsal surface of the head by small conical pores.
The stalk of the carpocephalum is up to 20 mm. in height with a few colourless or brown scales on the ventral side. The semicircular head is deeply cleft into four or sometimes into eight segments, the segments themselves being bilobed. The lobes are curved downwards slightly and tend to be keel-shaped below. One sporogonium matures to each lobe. Surrounding the sporogonium is a calyptra which withers at an early stage, a transparent pseudoperianth and a well-developed involucre. The involucre arises from the margin of the lobe. It takes the form of an obliquely-placed cylindrical sheath with a narrow bilabiate opening on the outer ventral edge. The lips are at first closed together (Fig. 3b) but open apart as the capsule reaches maturity (Fig. 3c).
The spherical capsule is dark brown in colour. Its jacket is uniseriate with the cell walls strengthened by annular or half-ring shaped bands. The capsule dehisces by either r or 5 valves while still within the involucre, the valves being held in position by the perianth. Later, as the spores are being shed, the stalk elongates carrying the capsule outside the perianth and outside the involuere; the valves now split apart to the base and spread out flatly as an attractive dark-brown star lying against the green involucre (Fig. 3d). The elaters have two spirals of thickening. They vary in length from 240 to 625μ and taper gradually to a point at either end from a maximum width of 9μ. The spores are unicellular,
18–25μ in diameter. The outermost part of the wall takes the form of a broad wing which becomes wrinkled when the spore is dry.
A further paper is being published in which the details of structure and development will be described and affinities between the above species and other Hepaticae will be discussed.
The writer is indebted to Mrs. M. G. Tetley for the lining-in of Figures 1 and 2 and to Mrs. E. A. Hodgson for checking that the liverwort in question had not been described previously.
Tansley, A G. and Chipp, T. F., 1926. Aims and Methods in the Study of Vegetation. London.