Arcangeliella scissilis , a rare American semihypogeous fungus

The study of the hypogeous Russulales has been a subject of great interest for the senior author in the last years (Moreno-Arroyo et al. 1998a, b; Calonge, Vidal 1999, 2001; Moreno-Arroyo et al. 1999; Calonge, Martín 2000; Vidal et al. 2002). The presence of Arcangeliella scissilis in Costa Rica has been reported a few years ago (Calonge, Mata 2005), and now we are trying to give some new information on this very rare species.


INTRODUCTION
The study of the hypogeous Russulales has been a subject of great interest for the senior author in the last years (Moreno-Arroyo et al. 1998a, b;Calonge, Vidal 1999, 2001;Moreno-Arroyo et al. 1999;Calonge, Martín 2000;Vidal et al. 2002).
The presence of Arcangeliella scissilis in Costa Rica has been reported a few years ago (Calonge, Mata 2005), and now we are trying to give some new information on this very rare species.

MATERIAL AND METHODS
Central ameriCa.Costa Rica: Guanacaste, Bagaces, Área de Conservación Arenal, Sector Finca Rio Naranjo, Collection consisted in 18 basidiomes, which appeared closely aggregated being difficult to separete each other, due to be partially melted at the base (Fig. 1).No specific smell or taste was appreciated in fresh.They were growing semihypogeous in riparian forest soil, under Quercus sp., 24-V-1999, leg.Isaac López.INB 1545920.
After the field observation, the material was studied in the laboratory under the light microscope, using 3% KOH as liquid medium and observed in a Nikon Labophot.For SEM a spore deposit was coated with gold and observed in a Hitachi S-3000N, belonging to Real Jardín Botánico of Madrid.Zeller & C.W. Dodge, Ann. Mo. Bot. Gard. 22: 369 (1935) ≡ Martellia scissilis (Zeller & C.W. Dodge) Singer & A.H. Sm., Mem. Torrey Bot. Club 21: 45 (1960).Basidioma globose to tuberiform, 23-35 mm diameter in fresh.Peridium smooth, cream with orange, to dark reddish tones.In wet weather the surfase changes to viscid or muscilaginose.The consistency of basidioma is solid, sofl in fresh conditions and coriaceus when dry, with venous surface.

Arcangeliella scissilis
Gleba partially exposed at base of basidioma, where a rudimentary prolonged stipe-like formation can be observed (Fig. 1).Gleba in section appears with a labyrinthic structure, with chambers 0.1-0.4mm diameter, full of spores, showing a cream colour when mature.Columella absent.Sections of the fresh basidioma exuding a white latex, which changes to lemon yellow in a few minutes.Smell and taste indistinct.

DISCUSSION
After a first look to the studied material, we thought that it was an Arcangeliella, due to the presence of an abundant white latex, rudimentary to absent stipe and a partially nude gleba at the base.Thanks to the excellent article published by Thiers (1984), on the genus Arcangeliella, it has been possible to include our material within this genus.
The material from Costa Rica was coincident with that of Zelleromyces gilkeyae (Singer, Smith 1960) that is why we decided to identify both taxa.Nevertheless, the problem of the genera delimitation in the Astrogastraceous is a big one, according to Singer and A.H. Smith (1960).The production of an abundant latex in fresh is a fundamental character in Zelleromyces, which makes possible the separation with Gymnomyces and Martellia, without latex.However, this character is difficult to observe when working with dry material or herbarium specimens.
Thus, Beaton et al. (1984) and Zhang and Yu (1990) have proposed, as a better character, the spore ornamentation.In this way, they suggest to include within the genus Zelleromyces only species with reticulate, subreticulate or winged spores.In Martellia those species with warty to spiny spores and in Gymnomyces all kind of spores; being possible the separation between the last two groups by the presence or absence of sphaerocyst nests, which are not always easy to locate.Thus, none of these methods is really functional.
Within this chaos, Vidal (2004) has been trying to get a reasonable explanation rediscribing the genus Arcangeliella (Cavara 1900) to which the genus Zelleromyces is synonymysed.Thus, within the actual Vidal´s concept, all the genera from the Astrogastraceous, lacking stipe or any rest of it, from the sterile base or columella, are included in Arcangeliella.This is the case of our material from Costa Rica.Other important characters, besides latex presence, are hymenial trama, generally homomerous; despite the possibility to observe some dispersed sphaerocysts, in A. scissilis.On the other hand the spores may be reticulate, subreticulate, warty, spiny, globose to ellipsoid.
At the same time, the other species with well-developed stipe and percurrent columella are included in a restored genus, Gastrolactarius R. Heim ex Vidal (Vidal 2004).
Regarding to molecular biology studies, carried out on this group, Miller et al. (2001) have demonstrated that Arcangeliella and Zelleromyces aligne within Lactar ius section, while Macowanites, Gymnomyces, Cystangium and Martellia do within Russula clades.
Concerning the ecology of Arcangeliella scissilis, as far as we know, it grows under Quercus sp.; other authors have collected it under Acer (Singer, Smith 1960), Alnus, Picea, Tsuga (Desjardin 2003) and in the case of the so named Martellia gilkeyae it was found under Corylus (Singer, Smith 1960).
Its geographical distribution, until now, was limited to West of USA (Desjardin 2003), thus, the Costa Rican collection should be the first record outside the United States.

CONCLUSIONS
Arcangeliella scissilis represents a rare taxon which is limited to Western United States and Costa Rica.It seems to be associate to various species of vascular plants, such as Acer, Alnus, Quercus, Picea, Tsuga and Corylus.
From the phylogenetic point of view, Arcangeliella fits well within the Lactarius clades.