Agaricus endoxanthus Berk. & Broome, J. Linn. Soc., Bot.

Chen, Jie, Parra, Luis A., Kesel, André De, Khalid, Abdul N., Qasim, Tayyaba, Ashraf, Aisha, Bahkali, Ali H., Hyde, Kevin D., Zhao, Ruilin & Callac, Philippe, 2016, Inter- and intra-specific diversity in Agaricus endoxanthus and allied species reveals a new taxon, A. punjabensis, Phytotaxa 252 (1), pp. 1-16 : 6-8

Agaricus endoxanthus Berk. & Broome, J. Linn. Soc., Bot. 11: 548 (1871) Fig. 3A–D

Notes:— Agaricus endoxanthus is a tropical species originally described from Sri Lanka ( Berkeley & Broome 1871). It is morphologically characterized by a dark greyish pileus, which can be fibrillose or usually radially and/or concentrically cracked, chrome yellow discolouration (at times only slightly) on the stipe base when cut or rubbed, spores with an average size of 5.2 × 3.3 μm, and pileipellis hyphae comprising elements distinctly constricted at the septa and with vacuolar pigment. In view of macro-morphology, such as pileus colour, yellowish discoloration when cut at the stipe base, A. moelleri sometimes is easily misidentified as A. endoxanthus ( Fig. 3E ). However, the former has larger basidiospores (5.8 × 3.7 μm on average) and its pileipellis hyphae comprise filamentous hyphae, rarely with some more inflated cells, and with diffuse pigment ( Kerrigan et al. 2005; Parra 2013). In addition, the distribution of A. moelleri has only been confirmed in non-tropical areas, in Europe and Iran so far (Mahdizadeh et al. in press; Parra 2013), while A. endoxanthus is either naturally distributed in tropical areas or introduced in local places with artificial tropical conditions. Agaricus rotalis , was described from Hawaii and is closely related to A. endoxanthus ( Kerrigan et al. 2005) . It was noted that the two species are morphologically indistinguishable, however, they were separable by their ITS sequence data ( Kerrigan et al. 2005). Recently, Parra (2013) synonymized A. rotalis with A. endoxanthus after reexamination of both holotypes and studies of extensive samples.

The characters such as pileus colour and the pileipellis type of disruption are shared morphological characters that can be observed in every specimen of the present study (see species notes below, Fig. 3E , Fig. 4 , 5 ), therefore, are of limited taxonomic value. Similarly, microscopic characters, such as spore size, cheilocystidia and pigment type did not allow us to distinguish specimens identified as A. rotalis from those identified as A. endoxanthus . Data for the above mentioned characters from 11 specimens are given in Table 3. The differences between the average spore sizes among different individuals are low and reflect intraspecific variation. On the other hand, the species-specific ITS markers proposed to circumscribe the two species ( Kerrigan et al. 2005) are no longer supported after addition of new samples ( Table 1).

Intraspecific variation is also remarkable among ITS 1+2 sequences of 14 collections of A. endoxanthus . The fact that the three European collections of A. endoxanthus genetically diverge from each other ( Fig. 2 ) strongly suggests that this species has been introduced several times independently in European tropical greenhouses where it might remain confined. This confirms the ‘frequent traveler’ status of this species which, therefore, might have been introduced or exchanged also between tropical countries following commercial plant exchanges since several centuries. Samples exhibiting numerous heteromorphisms might result from hybridization between samples that originate from divergent populations.

The two Thai samples (ZRL3094 and NTS07) which form a small divergent clade do not differ morphologically from the other samples, while they differ molecularly from all of them at the positions 481 and 519 of the ITS sequence. The number of differences between ITS sequences of closely related species of Agaricus is rarely less than three. When this is the case, it generally reflects intraspecific variability unless these differences are consistently correlated with a morphological difference. For example, sequences of A. moelleri and A. xanthodermus differ at two positions and their pileus consistently differs by the presence or absence of colored persistent scales, respectively ( Kerrigan et al. 2005). For the two samples ZRL3094 and NTS07 we do not find characteristic morphological characters; moreover the high number of polymorphic positions in A. endoxanthus suggests that these two differences reflect intraspecific variability. We do not have presently any pertinent reason for not including these two samples in A. endoxanthus .

Figures

FIGURE 2. Radial neighbor-joining (NJ) distance tree based on allelic polymorphism at 30 positions in the rDNA ITS region of 14 collections of A. endoxanthus. Regions: Caribbean (CAR), European tropical greenhouse (EUT), Hawaii (HAW), North America tropical greenhouse (NAT), and Southeastern Asia (SEA). Bootstrap values above 50% are shown.

FIGURE 3. Agaricus endoxanthus and A. moelleri. a. Overall structure of A. endoxanthus (ZRL3094). b. Overall structure of A. endoxanthus (LAPAM47). c. Strong yellow at base when cut (LAPAG225). d. Vacuolar pigment in pileipellis hyphae of A. endoxanthus (LD2012183). e. Overall structure of A. moelleri (LAPAM27).

FIGURE 4. Agaricus punjabensis (holotype). a–b. Sporocarps in situ. c. Basidia. d. Basidiospores. e. Cheilocystidia. f. Pileipellis. Scale bars: a–b = 1 cm; c, e = 5 μm; d = 2 μm; f = 20 μm.

FIGURE 5. Agaricus volvatulus. a–b. Overall structure (ADK2566). c. Strong yellow discolouration on stipe surface when bruised (ADK4266). d. Marginate bulbous stipe base (LAPAF5). e. Vacuolar pigment in pileipellis hyphae (ADK2566).