II. Marattiales (Eusporangiate isosporous Filicales).

The Marattiaceae, the single family of ferns included in the Marattiales, comprise the genera Angiopteris, Archangiopteris, Marattia, Danaea, and Kaulfussia, which are for the most part tropical in distribution. These genera are characterised by eusporangiate sori or synangia, the presence of stipules at the base of the petioles, and by the complex arrangement of the vascular tissue. In view of the fact that many fossil ferns show a close resemblance to the recent Marattiaceae, the surviving genera are briefly described. The prothallus is green and relatively large.

Angiopteris. This genus occurs in Polynesia, tropical Asia, and Madagascar; it is characterised by a short and thick fleshy stem bearing large bipinnate leaves which occasionally show a forking of the rachis[746], a feature reminiscent of some Palaeozoic fern-like fronds. One of the large plants of Angiopteris evecta in the Royal Gardens, Kew, bears leaves 12 feet in length with a stalk 6 inches in diameter at the base. The sessile or shortly stalked and rather leathery linear or broadly lanceolate pinnules have a prominent midrib and dichotomously branched lateral veins. The surface of an old stem is covered with the thick stumps of petioles enclosed by pairs of fleshy stipules ([fig. 241], A) and bears numerous fleshy roots, which hang free in the air or penetrate the soil. The young fronds ([fig. 220], A) exhibit very clearly the characteristic circinate vernation. The proximal part of each primary pinna is characterised by a pulvinus-like swelling. The sporangia, in short linear elliptical sori near the edge of the pinnules, consist of free sporangia ([fig. 242], A–D) provided with a peculiar type of “annulus”[747], in the form of a narrow band of thicker-walled cells, which extends as a broad strip on either side of the apex. An examination of sections through the sporangia of Angiopteris in different planes[748] illustrates the difficulty of determining the precise nature of the annulus in a petrified sporangium which is seen only in one or two planes. Many of the sporangia from the English Coal-Measures, compared by authors with those of Leptosporangiate ferns, are in all probability referable to the Marattiaceous type.

Fig. 241.

  1. Angiopteris evecta. (Considerably reduced.)
  2. Marattia fraxinea. Stipule. M.S.

The vascular system[749] of the stem constitutes a highly complex dictyostelic or polycylic type which may consist of as many as nine concentric series of strands of xylem surrounded by phloem, with large sieve-tubes and a pericycle which abuts on the parenchymatous ground-tissue without any definite endodermal layer. A peculiarity in the vascular strands is that the first-formed elements of the phloem lie close to the edge of the xylem, the metaphloem being therefore centrifugal in its development. The ground-tissue is devoid of mechanical tissue and is penetrated by roots, a few of which arise from the outer vascular strands while others force their way to the surface from the more internal dictyosteles. Leaf-traces, consisting of several strands, are given off from the outermost cylinder and a segment of the second dictyostele moves out to fill the gap formed in the outermost network, while the gap in the second cylinder receives compensating strands from the third. A few layers below the surface of the petiole there is a ring of thick-walled elements (s, [fig. 243]), and in both petiole and stem numerous mucilage ducts and tannin-sacs occur in the ground-tissue. It has been shown by Farmer and Hill[750] that in some of the vascular strands in an Angiopteris stem a few secondary tracheae are added to the primary xylem by the activity of the adjacent parenchyma. The vascular bundles in the petiole form more or less regular concentric series; they have no endodermis and are characterised also by the large size of the sieve-tubes (st, [fig. 243]).

Fig. 242.

(D, after Zeiller.)

The roots of Marattiaceous ferns ([fig. 244]) are characterised by the larger number of xylem and phloem groups; the stele is polyarch and not diarch, tetrarch or hexarch as in most Leptosporangiate ferns.

Fig. 243. Angiopteris evecta. Section of petiole (considerably reduced) and of a single vascular bundle (magnified): px, protoxylem; st, sieve-tubes.

Fig. 244. Angiopteris evecta. Transverse section of root, with part of the stele magnified: s, sieve-tubes; p, phloem; px, protoxylem.

Archangiopteris. This monotypic genus, discovered by Mr Henry in South Eastern Yunnan, was described by Christ and Giesenhagen in 1899[751]. The comparatively slender rhizome has a fairly simple vascular system[752]. The simply-pinnate leaves bear pinnules like those of Danaea, but the sori agree with those of Angiopteris except in their greater length and in the larger number of sporangia.

Marattia. This genus, which extends “all round the world within the tropics[753],” includes some species which closely resemble Angiopteris, while others are characterised by more finely divided leaves with smaller ultimate segments. The fleshy stipules occasionally have an irregularly pinnatifid form ([fig. 241], B). The sporangia are represented by oval synangia[754] ([fig. 245], A; the black patches at the ends of the lateral veins) composed of two valves, which on ripening come apart and expose two rows of pores formed by the apical dehiscence of the sporangial compartments ([fig. 245], A′, B). In Marattia Kaulfussii the sori are attached to the lamina by a short stalk ([fig. 245], B, B′) and the leaf bears a close resemblance to those of the Umbelliferous genera Anthriscus and Chaerophyllum. The vascular system is constructed on the same plan as that of Angiopteris but is of simpler form.

Fig. 245.

(C, after Hooker; D, E, after Schimper.)

Danaea. Danaea, represented by about 14 species confined to tropical America, is characterised by simple or simply pinnate leaves with linear segments bearing elongated sori extending from the midrib almost to the margin of the lamina. Each sorus consists of numerous sporangia in two parallel rows united into an oblong mass partially overarched by an indusium ([fig. 242], E, i) which grows up from the leaf between the sori. In the portion of a fertile segment shown in [fig. 242], E, the apical pores are seen at a; and at b, where the roof of the synangium has been removed, the spore-bearing compartments are exposed. The vascular system[755] agrees in general plan with that characteristic of the family.

Kaulfussia. The form of the leaf (Vol. I. p. 97, fig. 22) closely resembles that of the Horse Chestnut; the stem is a creeping dorsiventral rhizome with a vascular system in the form of a “much perforated solenostele[756].” The synangia are circular, with a median depression; each sporangial compartment opens by an apical pore on the sloping sides of the synangial cup ([fig. 245], C)[757].

Copeland has recently described a Marattiaceous leaf which he makes the type of a new genus, Macroglossum alidae. The sori are nearer the margin than in Angiopteris and are said to consist of a greater number of sporangia. The photograph[758] of a single pinna which accompanies the brief description hardly affords satisfactory evidence in support of the creation of a new genus. The structure of a petiole which I have had an opportunity of examining, through the kindness of Mr Hewitt of Sarawak, shows no distinctive features.