Monoicomyces Thaxt.

Santamaria, Sergi & Pedersen, Jan, 2021, Laboulbeniomycetes (Fungi, Ascomycota) of Denmark, European Journal of Taxonomy 781, pp. 1-425 : 326-328

Genus Monoicomyces Thaxt.

MB#3254

Proceedings of the American Academy of Arts and Sciences 35: 412 ( Thaxter 1900). –

Type species: M. homalotae Thaxt.

Brief description

Monoecious. Receptacle three-celled. Cell II supports one to several secondary axes (also known as secondary receptacles). Cell III in contact or not with cell I. Secondary axes consist of one to many superposed cells, derivatives from cell II, giving rise to antheridia and perithecia. The antheridia have been defined as of the compound type because their complex structure, which consists of 3–4 tiers of paired cells, where the 2 nd or 2 nd + 3 rd tiers, respectively, bear the phialides. The antheridia also bear the secondary sterile appendages. Perithecium with four cells in each vertical row of outer wall cells.

Remarks

The genus consists of 53 species (including the four described here), of which 24 in Europe, 15 in Denmark. The most recently described species is M. drusillae ( Santamaria et al. 2020a) . The genus was described by Thaxter (1900) for species “showing a bicellular receptacle bearing fertile and sterile branches”, where the fertile branches were regarded essential to delimit the genus at a time where only four species were known: M. homalotae , M. britannicus , M. sanctae-helenae and M. invisibilis . The description of this genus left open questions related to understanding the exact organization of three elements in the thallus: i.e., the primary receptacle, the primary appendage, and the antheridia. The first two are related because the primary appendage is separated from the primary receptacle by the primary septum. Therefore, determining the location of the primary septum is crucial. According to Majewski (1994b), the primary receptacle may be two- or three-celled. We question this judgement and consider the receptacle invariably three-celled. The problem is that what some authors have described as “the basal cell of primary appendage” or simply “the appendage” is in fact the cell III.

The third issue refers to the antheridial structure. Inside the compound antheridia we find the spermatiaforming cells or phialides following the terminology of Tavares (1985). In Monoicomyces , this is a rather complex structure which usually consists of four tiers of cells: a 1 st tier with a pair of sterile cells at the base, 2 nd and 3 rd tiers each consisting of a pair of sterile cells that support several flask-shaped phialides pointing to a central cavity, and a 4 th tier with another pair of sterile cells. The first tier is supported by one ± long stalk consisting of one to a few cells which form the secondary receptacle, resulting from a division of cell II. The 4 th tier typically bears secondary sterile branches in a variable number (1–4). Second and 3 rd tiers are the most difficult to explain and understand. Some species reduce these two tiers to only one, but most species have two. The number of phialides may vary from (2–)4 to 8 for each antheridium. We suggest that this characteristic may be used to distinguish some species as, for example, M. homalotae from M. britannicus . But this area of the antheridium is even more complicated by the presence of several sterile cells which build an outer wall delimiting a central cavity where spermatia are released from phialides before being discharged through a pore located between secondary sterile appendages ( Santamaria et al. 2020a).

Key to the Danish species

1. Thallus with a bilateral or symmetrical organization, with a fan-like disposition of antheridia and perithecia. Antheridia appear to be terminal because perithecia arise underneath and laterally from stalk cells of secondary axes. On Col. Staphylinidae Aleocharinae ................................................. 2

– Thallus with a unilateral, asymmetrical organization. Antheridia situated laterally on the axis of the secondary receptacle which terminates with a single perithecium (some thalli may undergo branching showing almost bilateral patterns, but always one perithecium is on the top). On Col. Staphylinidae Oxytelinae ....................................................................................................................................... 13

2. Outer surface of antheridia blackened .............................................................................................. 3

– Outer surface of antheridia not blackened........................................................................................ 6

3. Thallus consisting of two secondary axes, each with 2–4 superposed cells giving rise to antheridia and perithecia in a unilateral series all pointing towards the inner margin. On Bolitochara Mannerheim, 1830 (Col. Staphylinidae Aleocharinae )............................................... M. bolitocharae T.Majewski

– Thallus consisting of two to several secondary axes, each with only one cell giving rise to one antheridium and one perithecium ..................................................................................................... 4

4. The appendages above cell III ± branched, darkened, very elongate and exceeding the perithecial apices. On Ocalea Erichson, 1837 (Col. Staphylinidae Aleocharinae ) ............ M. fragilis Scheloske

– The appendage above cell III unbranched........................................................................................ 5

5. Cell VI large, strongly broadened distally, then abruptly constricted below cell VII and perithecial basal cells. Basal cell of primary appendage bulging towards the inner margin and separated by strongly constricted septa from cells above and below. On Oxypoda Mannerheim, 1830 (Col. Staphylinidae Aleocharinae ).................................................................................. M. crassicaulis Santam. sp. nov.

– Characteristics not as above. On several genera of Col. Staphylinidae Aleocharinae ......................... .......................................................................................................................... M. nigrescens Thaxt.

6. Perithecial stalk cell (cell VI) with narrower and darkened lower half............................................ 7

– Perithecial stalk cell (cell VI) neither narrower nor darkened........................................................ 12

7. Perithecia bearing a horn-like protuberance near the apex. On Gnypeta (Col. Staphylinidae Aleocharinae )..................................................................................... M. reboleirae Santam. sp. nov.

– Perithecia without protuberances...................................................................................................... 8

8. Secondary appendages absent or reduced to only one initial for each antheridium. Perithecium hamshaped in side view. On various Aleocharinae (Col. Staphylinidae )...................... M. athetae Thaxt.

– Secondary appendages well-developed. Perithecium not ham-shaped ............................................ 9

9. Cell III supporting the unbranched primary appendage only. Cell VI very elongate, up to three times the perithecial length. On Myllaena Erichson, 1837 (Col. Staphylinidae Aleocharinae ).................... ........................................................................................................................ M. myllaenae Santam.

– Cell III supporting the primary appendage and another branch below and next to it..................... 10

10. Fourth antheridial tier consisting of two prominent, auricle-like cells; bearing 2–4 short secondary appendages, which do not exceed in length the perithecial apices. Cell VI forming an almost right angle with the base of the perithecium. On Drusilla Leach in Samouelle, 1819 (Col. Staphylinidae Aleocharinae ).................................................................................................... M. drusillae Santam.

– All the above characters not found together .................................................................................... 11

11. Appendages on cell III very elongate, exceeding in length the perithecial apices; the dorsal branch (i.e., the primary appendage) darkened, especially towards the dorsal margin. Base of primary appendage wrinkled. Antheridia slender, with the 4 th tier not prominent, bearing two long secondary appendages arising close together, and then diverging strongly. On Ocyusa Kraatz, 1856 and Atheta (Col. Staphylinidae Aleocharinae ).................................................... M. brachiatus Santam. sp. nov.

– Appendages on cell III short. Base of primary appendage smooth. Antheridia stocky, with a prominent 4 th tier, bearing short secondary appendages. On Atheta and Geostiba Thomson, 1858 (Col. Staphylinidae Aleocharinae ).......................................................... M. validus Santam. sp. nov.

12. Cell III pale, in contact with cell I; supporting the primary appendage where the basal cell is darkened and strongly narrowed. Four phialides for each antheridium.......................... M. britannicus Thaxt.

– Cell III dorsally darkened; supporting the primary appendage where the basal cell is usually darkened, but separated from cell III by a not narrowed, paler septum. Eight phialides for each antheridium....................................................................................................... M. homalotae Thaxt.

13. Perithecium asymmetrical and bent. Secondary appendages absent or very reduced. On Platystethus arenarius (Geoffroy, 1785) (Col. Staphylinidae Oxytelinae ) .................... M. matthiatis T.Majewski

– Perithecium symmetrical and straight. Secondary appendages present, usually ± elongated. On Oxytelus , Anotylus , Aploderus and Platystethus (Co. Staphylinidae Oxytelinae )............................... ............................................................................................................................ M. invisibilis Thaxt.