Agaricus sp.

Parra, Luis A., Angelini, Claudio, Ortiz-Santana, Beatriz, Mata, Gerardo, Billette, Christophe, Rojo, Carlos, Chen, Jie & Callac, Philippe, 2018, The genus Agaricus in the Caribbean. Nine new taxa mostly based on collections from the Dominican Republic, Phytotaxa 345 (3), pp. 219-271 : 252-254

Agaricus sp. LAPAM 48 from hybrid origin. ( Fig. 15 )

Macroscopic description: This collection consists of a single immature carpophore with white lamellae completely matching with the collections studied of A. rufoaurantiacus .

Microscopic description: Spores 4.53–4.78–4.94(–5.15) × 3.10–3.44–3.71 μm, Q=1.29–1.42–1.5, ellipsoid, smooth, brown, without apical pore. Basidia 16–23 × 6–9 μm, tetrasporic, clavate or slightly truncated at the apex, sterigmata up to 3 μm long. Cheilocystidia hyaline, usually simple, sometimes septate at the base, with terminal elements mostly pyriform, less frequently clavate, 8–22 × 7–12 μm; anteterminal elements in the septate ones globose to cylindrical of 5–9 × 5–7 μm. Pleurocystidia not observed. Lower surface of the annulus composed of hyaline hyphae, cylindrical, not or slightly narrowed at septa, 3–7 μm wide. Inflated elements not observed. Pileipellis a cutis, with transition to trichoderm in the squamulose disc. In the disc predominate cylindrical hyphae narrower at septa with short elements of 3–8 μm wide, some very scattered vesiculose elements up to 19 μm wide and terminal elements abundant, cylindrical or progressively attenuated towards the rounded apex, and outside of the disc predominate cylindrical hyphae with constant diameter composed of long elements 2–7 μm wide. In water, all hyphae contain abundant granular pigment (more in the disc), with golden yellow granules of up to 3 μm wide. Clamp connections not observed.

Macrochemical reactions: Schäffer’s reaction positive, slow but intense, dark reddish purple red. KOH reaction difficult to read because of the orange yellow color of the exsiccatum.

Material examined: DOMINICAN REPUBLIC, Distrito Nacional, Santo Domingo de Guzmán, Jardín Botánico de Santo Domingo, 25 November 2014, JBSD 126479 ( LAPAM 48).

Taxonomic comments: This collection is morphologically indistinguishable from the Dominican collections of A. rufoaurantiacus studied in this work.

Additional comments: LAPAM 48 is a wild sample closely related to A. sp. RMC-1256, A. sp. RMC-1257 and A. rufoaurantiacus . The ITS sequences of the samples of these entities are compared at 12 variable positions in Table 7. In an alignment of DNA sequences, we consider that two samples strictly differ at one position when they do not share any character (indel or nucleotide) at the homologous positions, and that samples of Agaricus which differ at more than two positions generally belong to different species (Zhao et al. 20011) with few notable exceptions such as A. subrufescens ( Chen et al. 2016a) . The samples RMC-1256 and RMC-1257 differ at four positions and thus may belong to two closely related sister species. Two of the four positions, 517 and 520, are shown in Table 7 while at the two remaining positions, which are not shown, RMC-1257 differs from all the other samples compared in the Table. Moreover, this pair of samples differs from all ten collections of A. rufoaurantiacus at 11 of the 13 positions indicated in Table 7. This strongly indicates that A. rufoaurantiacus is a distinct species. LAPAM 48 is heteromorphic at 11 of these 13 positions where it exhibits two nucleotides: one also found in A. rufoaurantiacus and the other one found in the couple of samples RMC-1256 and RMC-1257. In fact, LAPAM 48 has a total of 15 heteromorphisms but four are at positions that are not shown in Table 7 because all the other samples are identical at these positions. Although the ten samples of A. rufoaurantiacus does not exhibit any heteromorphisms at 12 of the 13 positions of the Table 7, there is an intraspecific variability at positions that are not reported in this table because they are phylogenetically uninformative. Indeed, the ten samples of A. rufoaurantiacus possess on average 3.5 heteromorphisms at various positions where LAPAM 48, RMC-1256 and RMC-1257 have identical nucleotides. When we compared the whole sequences in detail, we noted that the ITS sequence of LAPAM 48 strictly differs (i.e. without shared allele) from the samples LAPAM 30 of A. rufoaurantiacus and RMC-1256 (A. sp.) at zero and one position (193), respectively. In contrast, RMC-1256 and LAPAM 30 differ from each other at 11 positions (all indicated in Table 7). These comparisons strongly suggest that an event of hybridization between A. rufoaurantiacus and a distinct species such as the species to which RMC-1256 belongs may have generated an unexpected combination of ITS sequences in LAPAM 48 or in one of its ancestors.

Figures

FIGURE 15. Macroscopic characters of Agaricus sp. LAPAM 48 from hybrid origin. A–B. Basidiomata (JBSD126479). B. Schäffer’s reaction on dried material. Above: pileus surface, below: stipe base. Microscopic characters of Agaricus sp. LAPAM 48 from hybrid origin. C–J. (C–H, J in ammoniacal Congo red; I in water). (JBSD126479). C–D. Cheilocystidia. E–F. Basidia. G. Spores. H. Hyphae of the lower surface of the annulus. I–J. Pileipellis hyphae. Photos by C. Angelini (A) and L.A. Parra (B–J).