Monoicomyces invisibilis Thaxt.

MB#189243

Figs 87, 88A–C

Proceedings of the American Academy of Arts and Sciences 35: 414 (Thaxter 1900). – Eumonoicomyces invisibilis (Thaxt.) Thaxt. (Thaxter 1901b: 21) [MB#245519]. –

Type: “On Homalota putrescens Woll., British Museum, No. 412, Azores”; FH. [This is a mistake because Thaxter exactly repeated the type of M. homalotae . Thaxter (1931: 43) reported that the type material is scanty, in bad condition and erroneous in relation to the host reference which is not Homalota but Oxytelus . The material reported in this latter work as a “locotypic indication” included: on Oxytelus hostilis Bernh. Nos. 3339 and 3452 from Fort de Koch, Sumatra, figures 3 and 6; on O. sulcifer Fauv., No. 3393, from Los Chorros, Venezuela.]

Eumonoicomyces californicus Thaxt. (Thaxter 1901b: 22) [MB#245492]. – Monoicomyces californicus (Thaxt.) Thaxt. (Thaxter 1931: 38) [MB#259377]

Eumonoicomyces argentinensis Speg. (Spegazzini 1912: 188) [MB#139851]

MonoicomYces affinis Speg. (Spegazzini 1915b: 65) [MB#186507]

Monoicomyces furcatus Thaxt. (Thaxter 1931: 41) [MB#265593]

Monoicomyces oxyteli Huldén [MB#108233], syn. nov. (Huldén 1983: 61, as M. oxytelis [MB#271607])

Diagnostic features

Receptacle consisting of a basal cell (I) supporting 2–12 flattened cells oriented diagonally which are cell II derivatives; the uppermost cell bears a solitary perithecium. Antheridia and sterile appendages borne laterally on cells of the main axis. Compound antheridium consisting of three tiers of paired cells (Fig. 88A–C), the 2 nd tier giving rise to four phialides (Fig. 88B, an), the 3 rd bearing (2–)4 secondary sterile appendages which are variable in length and pigmentation (Fig. 88A, C, bc sap1 and bc sap2). [Detailed descriptions: Thaxter 1908; Santamaria 1989; Majewski 1994b]

Distribution and hosts

Widely distributed in Europe (Czech Republic, Finland, France, the Netherlands, Italy, Norway, Poland, Spain, Sweden, Russia), America (Argentina, Guatemala, Haiti, Jamaica, Uruguay, USA, Venezuela), Asia (Sumatra) and Azores Islands (Santamaria et al. 1991), on Oxytelus, Anotylus, Aploderus and Platystethus (Col. Staphylinidae Oxytelinae) beetles usually found in herbivore dung. Further records not included in Santamaria et al. (1991): Belgium (De Kesel & Haghebaert 1991), United Kingdom (Weir 1996), China (Shen & Ye 2006), Ecuador (Proaño Castro & Rossi 2008), and Slovakia (Rossi et al. 2019b).

Collections examined from Denmark

On Anotylus inustus (Gravenhorst, 1806) (Col. Staphylinidae Oxytelinae) DENMARK – Fyn (F) • Gyldenstens inddaemmede Strand; 55°34.447′ N, 10°7.211′ E; NG75; 2 Apr. 2014; JP 689; JP det.; ZMUC C-F-123177 • Kratholm ved Bellinge; 55°19.710′ N, 10°19.335′ E; NG83; 18 May 2016; JP 89; JP det.; ZMUC C-F-122564 . – Sydsjaelland (SZ) • Bimose i Broby Overdrev; 55°23.921′ N, 11°35.499′ E; PG64; 1 Jul. 2013; JP 197; JP det.; ZMUC C-F-122676 .

On Anotylus sculpturatus (Gravenhorst, 1806) (Col. Staphylinidae Oxytelinae) DENMARK – Lolland, Falster, Møn (LFM) • Krenkerup Haveskov; 54°46.408′ N, 11°39.955′ E; PF77; 8 Jul. 1993; S. Langemark & O.E. Meyer 908; JP det.; ZMUC C-F-123406 . – Nordøstsjaelland (NEZ) • Klinten ved Selsø; 55°44.158′ N, 11°59.634′ E; PG88; 11 Mar. 2007; JP 520; JP det.; ZMUC C-F-123003 • Ledøje; 55°42.601′ N, 12°17.977′ E; UB37; 18 Apr. 2018; JP 1047; JP det.; ZMUC C-F-123563 • Tokkekøb Hegn; 55°52.334′ N, 12°22.229′ E; UB39; 6 May 2013; JP 332; JP det.; ZMUC C-F-122810 .

On Oxytelus fulvipes Erichson, 1839 (Col. Staphylinidae Oxytelinae) DENMARK – Østjylland (EJ) • Ørnsø ved Silkeborg; 56°9.446′ N, 9°31.488′ E; NH32; 20 May 2013; JP 380; JP det.; ZMUC C-F-122863 . – Lolland, Falster, Møn (LFM) • Lysemose ved Maribo; 54°46.971′ N, 11°28.959′ E; PF57; 4 Jun. 2018; JP 1130; JP det.; ZMUC C-F-123653 . – Nordøstsjaelland (NEZ) • Indelukket ved Frederiksborg Slot; 55°56.191′ N, 12°17.861′ E; UC30; 12 Apr. 2016; JP 3; JP det.; ZMUC C-F-122473 • ibid.; 19 Mar. 2017; JP 672; JP det.; ZMUC C-F-123161 • Stampeskov ved Rådvad; 55°48.332′ N, 12°33.138′ E; UB48; 23 Mar. 2017; JP 467; JP det.; ZMUC C-F-122951 . – Nordvestsjaelland (NWZ) • Nordbredden af Skarresø; 55°39.425′ N, 11°22.998′ E; PG47; 1 May 2013; JP 849; JP det.; ZMUC C-F-123344 .

On Platystethus alutaceus Thomson, 1861 (Col. Staphylinidae Oxytelinae) DENMARK – Sydjylland (SJ) • Juvre; 55°11.050′ N, 8°33.568′ E; MG71; 8 Mar. 2020; JP 1641; JP det.; ZMUC C-F-124369 .

On Platystethus arenarius (Geoffroy, 1785) (Col. Staphylinidae Oxytelinae) DENMARK – Lolland, Falster, Møn (LFM) • Jydelejet, Møns Klint; 54°59.171′ N, 12°31.954′ E; UA49; 2 May 2018; JP 1096; JP det.; ZMUC C-F-123613, C-F-123614 . – Vestjylland (WJ) • Skallingen; 55°31.076′ N, 8°14.838′ E; MG55; 28 May 1955; U. Kornerup Dry0114; U. Kornerup det.; ZMUC C-F-124181 • Tipperne; 55°52.452′ N, 8°14.261′ E; MG59; Oct. 1973; E. Rald Dry0113; E. Rald det.; ZMUC C-F-124180 .

Other material examined

Type of Eumonoicomyces papuanus

PAPUA NEW GUINEA • “ Eumonoicomyces papuanus, two slides from FH, #2092, barcode 00313728, and #2195, barcode 00313729, type, all over Oxytelus, from Ralum, prope New Guinea, New Pomerania (Papua New Guinea), ex Berlin Museum coll. no. 1012”; FH[00313728] [slide #2092 consists of five mature thalli in poor condition; slide #2195 consists of seven mature thalli in very poor condition, buried by crystals]

Remarks

First record from Denmark. Monoicomyces invisibilis is mostly accepted as a variable species. It may be a collective species, with discrepancy of opinions among the different authors as to which species should be placed among the synonyms.

In the protologue, Thaxter (1900) described small thalli (110–140 µm) with three receptacular cells or axial receptacle cells (i.e., those intermediate cells located between cell I and cell VI, derivatives from cell II; see Fig. 87A). The species was shortly after transferred to Eumonoicomyces by Thaxter (1901b). Years later, Thaxter (1931) again reallocated it to the genus Monoicomyces because of the characteristics of the phialides which are arranged in a single tier instead of two as for Eumonoicomyces . As described below, this two-tiers arrangement of phialides in Eumonoicomyces is not seen in the type slide (Fig. 88E, an). Moreover, Thaxter had doubts about the structure of the antheridia because of the difficulty of observing them in an adequate alignment. Also, he corrected some aspects of the type material (see above under the Type paragraph), and reduced M. affinis (Spegazzini 1915b) to synonymy with M. invisibilis .

At this point it seems quite appropriate to take a look at the genus Eumonoicomyces . This genus was described byThaxter (1900) including two species: E. papuanus and E. californicus . The latter was quickly transferred to Monoicomyces by Thaxter himself (1901b). Monoicomyces invisibilis and Eumonoicomyces argentinensis (the latter now a synonym of the former) went through this genus. Only E. platystethi was added later as a second species (Thaxter 1931); no more species have been described in the genus until today. Seemingly, the only difference between Eumonoicomyces and Monoicomyces lies in the structure of the antheridium. According to its author, in Eumonoicomyces, the phialides are obliquely arranged in two rows, in an area which entirely replaces the 2 nd and 3 rd tiers of cells in the antheridia of most species of Monoicomyces . Our observations of the type slides do not agree with this conclusion.

It is necessary to review Thaxter’s writings to understand the uncertainty that pervaded his description. Thaxter (1908) wrote (sic): “the only material from which it is possible to form an approximately accurate idea of the structure of the antheridium in this genus is that of E. papuanus ”. Subsequently, in the same publication, Thaxter provided a very detailed explanation about the structure of the compound antheridium but admitted many doubts related to the inappropriate orientation of the antheridia, which he himself defined as a cause of confusion. We have borrowed the type of E. papuanus from FH (see above under “other material examined”). The two slides include 12 thalli in rather poor condition, variably squashed, showing some degree of cell shifting, apparently due to inadequate handling during slide restoration. Despite all the drawbacks, a patient study of these slides does not agree with Thaxter’ s description. Based on our observations, we conclude that the compound antheridium consists of three tiers: the 1 st tier includes a pair of cells, the 2 nd tier includes a pair of cells supporting about eight phialides (maybe more) arranged in a single row divided into two sets (Fig. 88E, an), the 3 rd and uppermost tier bears the secondary sterile appendages (Fig. 88D, bc sap) and delimits the opening through which the spermatia flow out (Fig. 88E, arrow). Some additional cells around the 2 nd tier level serve to separate the spermatia cavity from the outside (Fig. 88D, F), as in other species of Monoicomyces . The oblique orientation of antheridia easily leads to misunderstanding the real position of the cells.

According to these observations, there is probably no strong support for the distinction between Eumonoicomyces and Monoicomyces, either morphologically or phylogenetically (Goldmann & Weir 2018), but we prefer to be conservative because the material at our disposition, including the type, was in imperfect condition. Moreover, the absence of photographs in records of Eumonoicomyces after Thaxter’s description does not help at all to verify the identifications or to understand a structure thought confusing by Thaxter (1908) himself. Likewise, we cannot confirm the presence of E. papuanus in Denmark, which was reported by Rostrup (1916), also because none of the numerous specimens we have studied fits its description.

Another matter concerns the possible synonyms of M. invisibilis . Monoicomyces californicus (initially described in Eumonoicomyces by Thaxter 1901b) differs from M. invisibilis according to the original description by its dark sterile appendages, “as well as by other points of difference” as written by Thaxter (1901b). The Fig. 87E and G from Anotylus inustus represents two of such thalli. Monoicomyces furcatus was distinguished from M. invisibilis by the bifurcate condition, “although this species is subject to much variation in size and may rarely be simple, instead of furcate” as written by Thaxter (1931). Figure 87F from Anotylus sculpturatus represents one such, rather common, bifurcate thallus. Rossi (1975) already suggested the synonymy of M. furcatus and M. californicus under M. invisibilis because (1) the furcate condition of M. furcatus is very variable and not clearly delimitated, and (2) the appendages may vary from hyaline to dark brown (as the thalli of M. californicus would be) with all the intermediate degrees of shading. Recently, De Kesel et al. (2020) kept M. californicus separate from M. invisibilis . To conclude the discussion of probable synonymies, a third species, Monoicomyces oxyteli (Huldén 1983) was separated from M. invisibilis by showing more numerous and narrower receptacular cells. Majewski (1999) accepted the distinctiveness of this taxon by the difference in number of receptacular cells, 2–3(–4) in M. invisibilis against 4–12 in M. oxyteli, as well as because this latter is exclusively for Oxytelus fulvipes Erichson (Fig. 87B–C). This does not agree with our observations, either for the number of receptacular cells which is extremely variable, or for the supposed exclusivity of O. fulvipes (Fig. 87D represents a thallus with four axial cells found on Anotylus sculpturatus). We therefore suggest to include also M. oxyteli among the synonyms of M. invisibilis .