INTRODUCTION

Janczewskia Solms-Laubach, which is a parasitic red algal genus, is host-specific on members of Rhodomelaceae, particularly Laurencia complex Lamouroux and Chondria C. Agardh, at least in the field (Setchell 1914;Nonomura and West 1981;Apt 1987;Fujii and Guimarães 1999). This genus was established based on J. verruciformis Solms-Laubach from Naples, Italy (Solms-Laubach 1877). Since then, Janczewskia has been reported from the various localities around the world (Falkenberg 1901;Setchell 1914;Tokida 1947;Martin and Pocock 1953;Feldmann and Feldmann 1958;Saito 1971;Abbott and Hollenberg 1976;Chang and Xia 1978;Apt 1987). At present, eleven species are accepted in the genus (Guiry and Guiry 2022).

As in Laurencia complex, apical growing cell in Janczewskia is situated at the base of a pit in branches (Fujii and Guimarães 1999). The vegetative and reproductive structure is also basically similar to its host. This genus is characterized by wart-like thallus with coalescent branches to form a solid tissue. However, in some species, branches from the wart are projected more or less or are conspicuously free (Apt 1987;Fujii and Guimarães 1999). This kind of branch is not found in others (Setchell 1914;Apt 1987). In the species, the branches rarely project beyond the surface of the basal tubercle (Setchell 1914;Apt 1987).

Currently, Janczewskia is divided into three sections based on branch development (Setchell 1914;Chang and Xia 1978). The type section Janczewskia (Eujanczewskia) involves species essentially lacking free branches from a basal nodule, including the type species J. verruciformis, J. solmsii Setchell et Guernsey and J. meridionalis Martin et Pocock (Setchell 1914;Apt 1987). By the contrast, Heterojanczewskia Setchell involves species with simple free branches projecting from a nodule-like base, such as J. gardneri Setchell et Guernsey, J. moriformis Setchell and J. lappacea Setchell, J. tasmanica Falkenberg, J. hawaiiana Apt, and J. morimotoi Tokida (Setchell 1914;Apt 1987). In the third section Stipitijanczewskia Chang et Xia, the species with radiating compound free branches without a distinct basal nodule, J. ramiformis Chang et Xia and J. tokidae Saito, are included (Chang and Xia 1978;Apt 1987).

However, this taxonomic scheme for the adelphoparasitic genus should be reconsidered, because the distinguishing features of branch development are variable (Nonomura and West 1981, the present study), and its host plants, such as Laurencia and Osmundea Stackhouse, show significant differences between them in fundamental vegetative and reproductive structures (Nam et al. 1994).

In this study, the vegetative and reproductive morphology of some Janczewskia species including the type species are examined based on specimens collected from various localities, and Heterojanczewskia stat. nov., together with an emendation of the generic delineation of Janczewskia, is proposed based on the features. Relevant nomenclatural changes for some Janczewskia species from California are also included.

MATERIALS AND METHODS

Data for this study were obtained from liquid-preserved and herbarium specimens of Janczewskia collected near Naples (type locality), the Mediterranean Sea (Italy) and Pacific (Korea, Japan, California and Australia). Liquid-preserved material was stored in a 10% solution of formalin/ seawater. For anatomical observations the material was cleared in 5-10% NaOH in distilled water for 2-7 days, then rinsed in distilled water. Branchlets dissected from the cleared material were longitudinally hand sectioned along the central axis, transferred to a slide with a drop of distilled water, and mounted in pure glycerin. For permanent slides, the glycerin was exchanged with 50% Karo^® corn syrup. Transverse section of branches 50-200 μm or thicker, depending on the degree of clearing, were also used to observe the development of vegetative, female and tetrasporangial structures. Axial development was studied in sections mounted in reverse on the slide. This was effective for the examination of pericentral cells in an axial segment. Measurements were given as length x diameter. Voucher specimens (Table 1) have been deposited in Herbarium of Department of Marine Biology, Pukyong National University, Korea.

RESULTS AND DISCUSSION

In Janczewskia gardneri, thallus is globular wart-like, 3.5- 4.5 mm in diameter, and parasitic on Osmundea spectabilis (Postels et Ruprecht) Nam from California (Fig. 1A and B). Coalesced branches arise conspicuously from a solid tissue (Fig. 1A) or are projected more or less as short protuberances (Fig. 1B).

Apical growing cell is located in the apical pit of branchlets, and successively cuts off axial cells. Each axial cell produces two pericentral cells giving rise to determinate growing filaments. Epidermal cells lack secondary pit connections between them, and show a non palisade-like arrangement in the transverse section of branches (Fig. 1C and D). Their size in ultimate branchlets is 10-23×18-33 μm. Lenticular thickenings are present in the medullary cells of male plants, but rarely observed in other sexual plants.

The urn-shaped apex of male branches is 690-890× 790-980 μm, with numerous spermatangial filaments derived from epidermal cells (Fig. 1E). Spermatangial filaments are terminated in a vesicular sterile cell with a relatively small size of 8×10 μm (Fig. 1F). Spermatangia are produced from the filaments (filament type), 8-10×4-5 μm, with a single apical nucleus (Fig. 1F and G).

In female plants, the apical pit of branchlets contains young procarp derived from trichoblasts. The central cell of young procarp with a trichogyne has five pericentral cells (Fig. 1H and I). Cystocarps are ovoid, 440-490×540-690 μm, without protuberant ostiole (Fig. 1J). Mature carpospores are clavate, 20-25×70-75 μm.

Stichidial branchlets are cylindrical, 640-740 μm in diameter. Tetrasporangia are produced from random epidermal cells, with two presporangial cover cells arranged parallel to stichidial axis and one postsporangial cover cell, and tetrahedrally divided (Fig. 1K). They show a parallel arrangement to stichidial axis, and are 86-100 μm in diameter.

In other examined species of Janczewskia including the type species J. verruciformis, J. morimotoi and J. tasmanica, thalli are wart-like with short protuberance or conspicuous free branches (Fig. 2A, F, L and M ), and epidermal cells are secondary pit-connected (Fig. 2B) and the vegetative axis has four pericentral cells. Spermatangia are produced from trichoblast in the apical cup-shaped pit of branches (Fig. 2C, G, H, I and N) (Trichoblast type: see Nam et al. 1994). Tetrasporangia arranged perpendicular or parallel to axis (Fig. 2E and J) are also derived from pericentral cells (Fig. 2D, K and O). The species with these spermatangial and tetraspermatangial features are parasitic on Laurencia, Chondrophycus (Tokida et Saito) Garbary et Harper, Palisada Nam or Chondria C. Agardh rather than Osmundea.

J. gardneri very differs from those species in reproductive features. As mentioned above, secondary pit connections are not found between epidermal cells and vegetative axial cells have two pericentral cells. As its host O. spectabilis, J. gardneri also has a filament type male structure (Nam et al. 1994) in the apical urn-shaped pit of branches rather than a trichoblast type, and tetrasporangial origin of epidermal cells rather than pericentral cells. These reproductive structures also appear to be found in J. moriformis and J. lappacea from California, particularly based on the original male description (Setchell 1914). However, these two species grow on Chondria rather than Osmundea (Abbott and Hollenberg 1976). As previously commented by Kurihara et al. (2010), this may indicate that those Janczewskia species evolved from Osmundea and that some of them switched hosts to Chondria after establishment of parasitism, based on the evolutionary scenarios of red algal parasites (Goff et al. 1996).

Considering the variable features of branch development (Nonomura and West 1981; the present study), these significant differences of vegetative and reproductive structures between those species could be importantly adopted for the taxonomy of Janczewskia. This strongly suggests that J. gardneri should be separated from the genus Janczewskia. In conclusion, the section Heterojanczewskia including J. gardneri, together with an emendation of the generic delineation of Janczewskia, is elevated to genus level and relevant nomenclatural changes (Table 2) for some Janczewskia species are proposed as follows:

According to Setchell (1914), J. tasmanica seems to belong to Sect. Heterojanczewskia. However, its reproductive features show those of Sect. Janczewskia (Figs. 2G-K). J. hawaiiana and J. morimotoi, which have been placed in Sect. Heterojanczewskia (Apt 1987), are also excluded from the section based on the male and tetrasporangial reproductive structure (Saito 1971, as J. tokidae; Apt 1987;Tokida 1947).

Heterojanczewskia (Setchell 1914) stat. nov.

Thallus parasitic; apical cell always sunk in an apical pit; central vegetative axis with two pericentral cells, recognizable only near apical cell; spermatangial structure with filament type (Nam et al. 1994) usually in apical urn-shaped pit; tetrasporangia produced from random epidermal cells.

Type species: H. gardneri (Setchell et Guernsey) comb. nov.

Type locality: California (Setchell 1914).

Basionym: Janczewskia gardneri Setchell et Guernsey in Setchell 1914: p. 12.

JanczewskiaSolms-Laubach (1877) gen. emend.

Thallus parasitic; apical cell always sunk in an apical pit; central vegetative axis with four pericentral cells, recognizable only near apical cell; spermatangial structure with trichoblast type (Nam et al. 1994) usually in apical cupshaped pit; tetrasporangia produced from particular pericentral cells.

Type species: J. verruciformisSolms-Laubach (1877).

Type locality: Naples, the Mediterranean Sea (Setchell 1914;Guriy and Guiry 2022).