Constancea 83, 2002
University and Jepson Herbaria
P.C. Silva Festschrift

On the Identity of Chorda rimosa Montagne (Phaeophyceae)

Aldo Asensi1, René Delépine2, Florence Rousseau3 and Bruno de Reviers3*
1 Rue du Moulinet, 18, F-75013 Paris, France
2 Villa Guibert, 2, F-75113 Paris, France
3 Institut de Systématique (MNHN, UPMC, CNRS-FR 1541),
Muséum National d'Histoire Naturelle, Laboratoire de Cryptogamie
12, rue Buffon, 75005 Paris, France
* Corresponding author (reviers@mnhn.fr)

figure of type packet
This paper is dedicated to Paul C. Silva on the occasion of his 80th birthday. René Delépine is particularly delighted to show his gratitude to Dr. Silva who, together with late Professor J. Feldmann, very kindly gave him advice during his first phycological research work on Codium ...some time ago (!). Bruno de Reviers is very grateful for all the advice kindly provided by Dr. Silva, and is also delighted to dedicate this article to him.

ABSTRACT

Syntype material of Chorda rimosa Montagne housed at PC was examined, and a lectotype designated in this study. This alga is not referrable to Chorda but rather to Adenocystis. This taxon is conspecific with the plants from New Zealand listed as Adenocystis sp. by Nelson (1994).

INTRODUCTION

Skottsberg (1907) made the combination Adenocystis utricularis (Bory de Saint-Vincent) Skottsberg, based on Asperococcus utricularis Bory de Saint-Vincent (1825 [‘1826’]) for material collected from the Falkland Islands (as ‘îles Malouines’) and Chilean coasts. Later, Skottsberg (1921) provided a more detailed account of this species and described the new form Adenocystis utricularis f. longissima which he considered might be conspecific with Chorda rimosa Montagne, as he wrote: “An = Chorda rimosa Mont” (The Latin conjunction “An” could be translated here either “isn't?” or “wouldn't it be?”). Chorda rimosa was placed in Scytosiphon by Endlicher (1843: 25) and in Tubicutis, a synonym of Scytosiphon, by Kuntze (1898: 434), these authors referring to Agardh's (1820) concept of Scytosiphon.

Adenocystis utricularis f. utricularis is known from the Falkland Islands, Patagonia, Tierra del Fuego and the Antarctic Peninsula, as well as from the South Orkney Islands, South Shetland Islands, South Georgia, Crozet, Kerguelen, Marion Island, Campbell Island, Auckland Islands, Chatham Islands, Macquarie Island, Stewart Island, southern New Zealand (Lindauer et al. 1961; Papenfuss 1964; Ricker 1987), and southern Tasmania (Cribb 1954; Womersley 1987).

According to Skottsberg (1921), Adenocystis utricularis f. longissima occurs in several localities in the southern South American regions of Patagonia, Tierra del Fuego, and the Falkland Islands. Skottsberg (1941: 37) also mentions this form from South Georgia (“Cumberland Bay, 23/iv/1902”).

Recently, an unidentified Adenocystis (“Adenocystis sp.”), was recorded from New Zealand by Nelson (1994) collected from the Bounty Islands as well as from the Antipodes, Auckland, and Campbell islands.

Therefore three taxa are currently included in the genus Adenocystis (1)Adenocystis utricularis f. utricularis with a very large geographical distribution; (2) Adenocystis utricularis f. longissima; (3) Nelson's Adenocystis sp.; the latter two with a much more restricted geographical distribution. Furthermore Chorda rimosa may belong to that genus as suggested by Skottsberg (1921) when he described Adenocystis utricularis f. longissima.

The aim of this study is to assess whether or not Chorda rimosa Montagne belongs to the genus Adenocystis and if so, to ascertain its relationships with the other species of the genus. For this purpose, syntype material of Chorda rimosa Montagne, housed at PC, was studied.

MATERIALS AND METHODS

Study of Chorda rimosa herbarium type material was made both using classical optical microscopy and Transmission Electronic Microscopy. For Adenocystis from New Zealand we received Xerox-copies of both “large” Adenocystis utricularis and “thin” Adenocystis sp. herbarium sheets as well as dry thalli of Adenocystis sp. on an herbarium sheet, collected from the Bounty Islands, associated with preserved slides made by D.G. Müller (see Fig. 10). Furthermore we were allowed to study a little piece of this material using histological techniques. Herbarium abbreviations follow Holmgren et al. (1990).

LECTOTYPIFICATION

Two syntype collections of Chorda rimosa are preserved in the Montagne Herbarium at PC, in two envelopes: (#MA 7475 and #MA 7476), both being annotated in Montagne's handwriting. Envelope #MA 7475 (Fig. 1) contains four fragments and is labeled “Chorda rimosa / Montag. / Voy. Pole Sud”. Envelope #MA 7476 (Fig. 2), is labeled “Chorda rimosa / Montag. / Auckland”", and contains fragments of several elongated thalli (Fig. 3); the latter, containing more complete thalli, is designated here as the lectotype collection. #MA 7475 (Fig. 1) is thus an isolectotype collection. In describing Chorda rimosa, Montagne (1842) mentioned that it was collected in Auckland Islands (“Hab. Ins. Auckland; d’Urville”), and specify (“Hab. in littore insularum Auckland ab ill. d’Urville inventa”) during the ‘Voyage au pôle sud’ (1845).

OBSERVATIONS

Chorda rimosa

In his original description of Chorda rimosa, Montagne (1842) stated: “fronde carnoso-membranaceâ nigrâ tubulosâ contortâ intùs non septatâ spiraliter plicato-rugosâ hinc indè rimis pertusâ, filis clavatis simplicibus et articulatis basi sporam obovatam gerentibus totâ vestitâ. —Hab. Ins. Auckland; d’Urville”. He gave a more complete description in Montagne (1845).

The material of C. rimosa (Figs. 1-3) appears fragmentary with no complete individual since no undamaged apex could be observed. For this reason and since no young thalli were available, apical growth could not be investigated. Fragments appear very elongated in gross morphology. The thallus is regularly cylindrical, only a few millimeters wide in this dry state. We did not rehydrate it in order not to damage further the only material currently known of this taxon. The contorted aspect, emphasized by Montagne (1842, 1845), is illustrated in his original drawing, preserved at PC under no. MS-435, p. 5055 (Figs. 4 and 5), and by Kützing (1858, vol VIII, Tab. 15 - text no. 2108 p. 7). The type material also shows this contortion clearly under the dissecting microscope, along with the tears that look like button-holes in Montagne's drawing Fig. 4 lower right); but the material is not well preserved and is difficult to study. However, transverse (Fig. 6) and longitudinal sections (Figs. 7-8) were made in specimens of the lectotype collection (Arrows, Fig. 3) and observed with a research microscope and TEM.

The thallus is hollow. In transverse section (Fig. 6) several zones were observed: (1) a fertile external region with paraphyses and sporangia; (2) a densely coloured zone formed of 1-3 layers of small isodiametric cells of 5-7 µm in studied specimens; (3) a colorless region formed by 5-8 layers of larger cells; and (4) a very thin region formed by compacted cell-structures, more or less reduced to their walls, bordering the central cavity.

In longitudinal section of adult thalli (Figs. 7-8), zones 1, 2, 3 described in transverse section can be easily recognized, but we can now interpret zone 4 as part of the network of inner longitudinal filaments formed by axially elongated cells which appear as an irregular internal zone in transverse section. These medullar longitudinally elongated filaments are shown by Montagne on an unpublished original drawing (Fig. 5), but the section shown seems to have been made in a young part of the thallus without the mature developed ‘network’. The medullar filaments appears in Kützing's plate of C. rimosa (1858, Tab. 15, figs. i, k). It must be pointed out that this network is quite different from the regularly arranged hyphae observed in Chorda (illustrated e.g., by Fritsch (1945: 222, fig I).

Sori of unilocular sporangia interspersed with paraphyses were very frequent in many sections (Figs. 6 and 7-8). Original drawings by Montagne (Fig. 4) of these paraphyses could give the impression that unicellular (white arrowhead) and multicellular (black arrowhead) paraphyses are present. Actually, we observed only unicellular organs, no multicellular ones. However their content appears sometimes fragmented and this is likely what Montagne (Fig 4) illustrated and the reason why he, erroneously, considered them multicellular. This could be also due to fertile epiphytes which are frequent on Adenocystis (Reviers and Delépine 1981). Within cells, TEM sections (Fig. 9) clearly show plastids containing thylakoids (white arrow) and a granular zone without thylakoids interpreted as a pyrenoid (asterisk).

Adenocystis sp. from New Zealand

It is amazing that, to our knowledge C. rimosa was not mentioned in the literature after its original description by Montagne (1842). However, Nelson (1994, p. 229) listed an Adenocystis sp. from the southern islands of New Zealand (Bounty, Antipodes, Auckland, and Campbell islands) as mentioned above. According to Nelson (18.xii.1996, pers. comm.) this species of Adenocystis does not appear to intergrade with A. utricularis f. utricularis. In WELT, herbarium specimens from Auckland and Campbell islands of both typical Adenocystis utricularis f. utricularis and Adenocystis sp. are preserved.

We examined herbarium specimens housed in WELT of this Adenocystis sp., collected at Penguin Island (Bounty Islands) and sent by W. Nelson, (Fig. 10). Gross morphology of these specimens resembles that of Chorda rimosa although they are smaller and do not appear contorted. In transverse sections, we observed the same structure as in C. rimosa with the same succession of different regions (Figs. 11, 12, 13, 14, 15. The vegetative regions of the mature thalli show 1-2 external epidermal layers of small pigmented cells and several cortical layers of larger and colorless cells. Their central region is hollow, surrounded by some vertical filaments formed of long, anastomosed cells, similar to what exists in Adenocystis utricularis and Chorda rimosa. In fertile regions, sporangia interspersed with paraphyses are present. The paraphyses and sporangia characters seem also similar in the two plants.

It is important to emphasize that even small plantlets of 2-3 mm are generally fertile. In these young individuals a transverse section shows an external layer of unicellular and claviform paraphyses with unilocular spororangia, similar to what is observed in Adenocystis utricularis f. utricularis and Chorda rimosa. At this step of development, the central region is filled by longitudinal filaments (Fig. 11) formed of long and anastomosed cells identical to what Delépine and Asensi (1978) described in Adenocystis plantlets, with, sometimes, the beginning of a central cavity (Fig. 12).

DISCUSSION

The placement of Chorda rimosa in Scytosiphon (or Tubicutis) by Endlicher (1843) and Kuntze (1898) was based on Agardh's (1820) concept of Scytosiphon (“Char. essent. Semina nuda pyriformia caudata superficiem exteriorem frondis totam obtegentia.”) which matched Chorda but which is not in accordance with the current concept of Scytosiphon.

Diagnostic characters of species and forms mentioned in this paper are summarized in Table 1. As regularly arranged medullary hyphae are not present in Chorda rimosa this species cannot be included in the genus Chorda. Moreover, paraphyses do not have mucilaginous thickened tops in Chorda (e.g., Kawai et al. 2000) whereas our specimens have paraphyses with mucilaginous thickened tops (Figs. 13, 14). On the other hand, anatomical, cytological, and reproductive structures of Chorda rimosa match Adenocystis quite well in organization and we believe that the Montagne species should be transferred to the latter genus. The formal combination will be proposed elsewhere.

Furthermore, morphological and structural characteristics of Adenocystis rimosa are very similar to those of Nelson's (1994) ‘Adenocystis sp.’ from the Bounty Islands, except the contorted aspect of ‘Chorda rimosa’. However, as pointed out by Fritsch (1945: 223): “When a piece of the thallus is allowed to dry, it becomes markedly contorted [. . .]”.We conclude that the difference in amount of contortion is probably not sufficient to separate the two and postulate that Chorda rimosa Montagne and Adenocystis sp. from New Zealand are conspecific.

ACKNOWLEDGEMENTS

Dr W. Nelson is gratefully acknowledged for sending photocopies of numerous specimens from WELT, and herbarium specimens of Adenocystis sp. and for allowing us to sample a small piece of this specimen for histological studies. Mr Jean Sourimant (Station Biologique de Roscoff), gave us large technical assistance for TEM studies, as well as Dr B. Dennetière (Muséum National d’Histoire Naturelle) who supplied very helpful assistance with histological preparations and photomicrographs. We thank Dr R. Moe for indicating two useful references that we had overlooked and for his careful reading of the manuscript.

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Table 1. Morphological and cytological characteristics of Adenocystis and Chorda.

      Taxon

Character

Adenocystis utricularis f. utricularis Adenocystis utricularis f. longissima Adenocystis sp. from New Zealand Chorda rimosa Genus Chorda
Length 10-20 cm reaching 1 m 5-10 cm 5-10 cm reaching 8 m
Gross morphology broad utricle long swollen utricle narrow regular tube narrow regular tube very long, terete whip-like thallus, hollow only in old parts
Growth apical apical apical apical ? intercalary
Medulla network network network network regularly arranged hyphae
Paraphyses with mucilaginous thickened top yes yes yes yes no
Pyrenoid present present present present absent