CAREX CAYOUETTEI (CYPERACEAE), A NEW INTERSECTIONAL SEDGE HYBRID FROM SOUTHERN QUÉBEC, CANADA - PDF

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Bergeron, A. and S. Pellerin Carex cayouettei (Cyperaceae), a new intersectional sedge hybrid from southern Québec, Canada. Phytoneuron : Published 2 June ISSN X CAREX

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Bergeron, A. and S. Pellerin Carex cayouettei (Cyperaceae), a new intersectional sedge hybrid from southern Québec, Canada. Phytoneuron : Published 2 June ISSN X CAREX CAYOUETTEI (CYPERACEAE), A NEW INTERSECTIONAL SEDGE HYBRID FROM SOUTHERN QUÉBEC, CANADA ALEXANDRE BERGERON and STÉPHANIE PELLERIN Institut de Recherche en Biologie Végétale Jardin botanique de Montréal, 4101 Sherbrooke Est Montréal, QC, H1X 2B2, CANADA ABSTRACT A putative hybrid of Carex (Cyperaceae) was discovered in a swamp in the Montréal region (southern Québec, Canada). A survey of the surrounding vegetation, numerical phenetic analysis, and use of proxies of plant sterility showed that the individuals were sterile intersectional hybrids between sects. Lupulinae and Vesicariae. We propose the name Carex cayouettei A. Bergeron, hybr. nov. for the hybrid combination C. comosa C. lupulina. Several factors (reproduction time, habitat and natural range) support the assumption that the hybrid is likely more common than suggested by previous knowledge, but difficulties encountered in identification may have limited documentation. This finding strengthens the evidence that Lupulinae and Vesicariae are closely related. An unidentified sedge was discovered near a swamp during a survey of an urban forest in the metropolitan Montréal area. The plant did not resemble any known species of the region; we thus suspected that it was a natural hybrid. Initially, Carex lupulina and C. pseudocyperus seemed to be possible parents (authorities are given in Appendix 1), since both were found in the swamp near the unfamiliar sedge. Such a combination was nevertheless questionable because intersectional hybrids between sects. Lupulinae Tuck. ex J. Carey and Vesicariae (Heuff.) J. Carey [combined with sect. Pseudocypereae (Tuck.) Christ sensu Ball & Reznicek 2002] are uncommon (Cayouette & Catling 1992). In addition, visual analysis of the characters was problematic, particularly in relation to size of vegetative organs, which did not appear intermediate. Although hybrid vigor exists among sedges, the intermediate state or presence of some characters more related to one of the parents is essential to the determination of legitimate intersectional hybrids such as C. lupulina retrorsa Schwein. (Dudley 1886; Cayouette & Catling 1992). We therefore examined the sedge vegetation around the unfamiliar plant more closely, and performed a phenetic analysis involving several other putative parents to determine which ones were involved in the hybrid combination. Study site The unidentified sedge was found at the Bois-de-Saraguay Nature-Park ( ' N, ' W), southern Québec, Canada. This Park is one of the best preserved urban forests on the Island of Montréal, not only because of restricted public access, but also because of its size (96 ha). This mature forest is characterized by a mosaic of mesic and hygric habitats with tree associations dominated by Acer saccharum, Fagus grandifolia, and Tilia americana on well-drained soils, swamps dominated by Acer saccharinum, and Fraxinus pennsylvanica on poorly-drained soils (Domon et al. 1986). In an exhaustive floristic survey (152 person-days) carried out by our research team between June and August 2011, a total of ca. 389 taxa were recorded, which represents a high level of richness for the region. Sedges accounted for a pool of 32 species (Appendix 1). Several rare Québec plants are only present in this park (Bergeron & Pellerin 2011; Bergeron et al. 2013). Despite low levels of past anthropogenic disturbances in this urban context, ca. 21% of florula is composed of naturalized and ephemeral plants. Bergeron and Pellerin: Carex cayouettei, intersectional hybrid 2 Fieldwork and laboratory During the plant survey of an open, flooded swamp on July 7, 2011, we collected the putative sedge hybrid for the first time. On July 14, 2011, we returned to the site to note all sedge species present in the swamp and within radii of 10 and 5 meters of the putative hybrid population. Macromorphological characters were measured in situ and ex situ on live specimens and those collected; the latter were then dried. Nine to twelve random measurements were taken for each character. In the laboratory, pollen grains were stained with cotton blue (lactophenol) to indicate defective cytoplasm. In order to collect the achenes, we examined the site closely a final time on October 16, Phenetic analysis After a summary examination of macromorphological measurements, we classified the putative hybrid as belonging to the group of bladder and bottlebrush sedges (sensu Hipp 2008). The specimens bore long and inflated perigynia, which distinguish the sect. Lupulinae and pistillate scales with scabrous awns characterizing, inter alia, the sect. Vesicariae. Furthermore, the broad vegetative blades on the putative hybrid could place it not far from the broadly construed sect. Paludosae (Heuff.) Christ (Ball & Reznicek 2002). For phenetic analysis, we first checked the sedge list for the Bois-de-Saraguay (Appendix 1) to select the putative parents among Carex sects. Lupulinae, Vesicariae, and Paludosae. We included species belonging to the three sections, with the exception of C. grayi (globular spikes) and C. pellita (pubescent perigynia), which have characters too distant from the putative hybrid. Second, we included five species forming hybrid combinations according to Cayouette and Catling (1992) and with documented occurrences in the Montréal region and southern Québec (A. Bergeron, unpub. data; Brouillet et al., 2010+). Carex lupuliformis Sartwell ex Dewey was not selected due to its rarity and remote populations well-researched in the context of the Pellerin s team s project, Rescuing false hop sedge (Environment Canada 2014). Finally, we included three species exhibiting some ornamental qualities, unlisted for Québec but possibly present due to escape from cultivation. In order of selection as described above, the 13 species are the following: C. intumescens, C. lacustris, C. lupulina, C. pseudocyperus, C. retrorsa, C. comosa Boott, C. hystericina Muhl. ex Willd., C. lurida Wahlenb., C. utriculata Boott, C. vesicaria L., C. acutiformis Ehrh., C. gigantea Rudge, and C. hyalinolepis Steud. Measurements of macromorphological characters related to the 13 possible parents were compiled from the literature (Gleason & Cronquist 1991; Hill 2006; Ball & Reznicek 2002; Jones 2010). Data analysis was performed by Principal Coordinates Analysis (PCoA) with Caillez correction (Legendre & Legendre 2012, p. 493) on the mid-point of min and max values of each character. The PCoAs were calculated on character tables rescaled in Gower s dissimilarity matrix (Legendre & Legendre 2012, p. 278), and then multiplied with an F-ratio weighting (Adams 1972, 1982). With the min and max values of each character, an F-ratio (intergroup variance intragroup variance) was calculated from an ANOVA between the species. Derived from the literature, these ranges of values establish the true boundaries of the species, which guarantees the validity of the calculations even if the intragroup variance were computed on only two degrees of freedom. In fact, we also tried the PCoAs without weighting (Adams 1972, 1982), which did not alter our conclusions. However, the weighting with the F-ratios gave the greatest amount of explained variance on the first two PCoA axes, which justified the use of this procedure. Note also that these numerical methods are not statistical hypothesis tests. We used the weighted PCoAs to synthesize information and draw a conclusion based on decisions. All analyses were performed using the R language (R core team, 2013). Bergeron and Pellerin: Carex cayouettei, intersectional hybrid 3 Preliminary analysis Eighteen selected characters known to discriminate sedges within and between the three sections were used (Table 1) in a preliminary analysis which aimed to reduce the number of putative parents to be examined in detail. By excluding the putative hybrid, we calculated F-ratios for weighting each of the 18 characters (Table 1). Ordination of the first two PCoA axes with the 14 taxa including the putative hybrid (80% of explained variance) made it possible to segregate sedge sections and identify species with characters too distant from the putative hybrid. All members of sect. Paludosae were discarded. We then calculated two other PCoAs that led to the successive removal of species distantly related to the putative hybrid. The last preliminary PCoA was performed on seven taxa (94% of explained variance) and placed the putative hybrid approximately in the middle of the PCoA axis I, the Lupulinae being on one side and Pseudocypereae [incl. within sect. Vesicariae] on the other. Triplet analysis To show the intermediate state of the putative hybrid relative to the characters of two sedge species, we only retained the six most likely parents (Carex comosa, C. gigantea, C. hystericina, C. intumescens, C. lupulina, and C. pseudocyperus) found in preliminary analyses. For the final analyses, we included 23 characters to improve refinement of the differences between taxa, and calculated new F-ratios (by excluding the putative hybrid) for weighting each of these characters (Table 1). By considering one species of sect. Lupulinae, the putative hybrid, and one species of sect. Pseudocypereae, we performed nine weighted PCoAs i.e., on all possible combinations of triplets. Table 1. Description of characters and units used in the phenetic analysis. The F-ratios calculated between the putative parents are also shown, i.e. with 13 species for preliminary analyses, and 6 species for triplet analyses. F-ratio for F-ratio for Characters 13 spp. 6 spp. 1. Culm length (cm) * Blade width (mm) * Number of prominent blade veins * Color of basal sheath (510 nm, 615 nm, 650 nm) * Number of terminal spikes * Sexuality of terminal spike (0: staminate, 1: bisexual) * Number of lateral spikes * Sexuality of lateral spike (0: pistillate, 1: bisexual) * Orientation of perigynium (45, 90, 135 ) * Orientation of proximal spike (45, 90, 135 ) * Perigynium length (mm) * Perigynium width (mm) * Perigynium length:width ratio Length of perigynium beak (mm) * Length of perigynium teeth (mm) * a Number of perigynium veins * Perigynium shape in cross section (0: trigonous, 1: round) * Apex of pistillate scale (0: acute, 1: acuminate, 2: awned) * Length of pistillate scale (mm) * NA Width of pistillate scale (mm) * NA Shape of beak teeth (0: straight, 1: outcurved, 2: very outcurved) * NA Width of proximal pistillate spike (mm) * NA Length of proximal bract (cm) * NA NA = Not applicable. * Characters measured directly on the putative hybrid. Data from Ball and Reznicek (2002), Jones (2010), Hill (2006), and Gleason and Cronquist (1991). a For C. gigantea, C. lupulina and C. intumescens, the length of perigynium teeth was measured in ImageJ (Rasband, 2012) on digital specimens after Bergeron and Pellerin: Carex cayouettei, intersectional hybrid 4 imaging improvements (range between spp.: mm); for each species, nine random specimens from AUA, TROY, USF, UWAL, or WIN herbaria (Thiers, 2008+) were used. RESULTS AND DISCUSSION The putative hybrid was discovered in a ca m 2 swamp that was home to 10 species of sedges. The companion vegetation was mainly composed of hydrophytes e.g., Alisma triviale, Impatiens capensis, Leersia oryzoides, Lemnoideae, and Onoclea sensibilis. In an area of 314 m 2 (10 m radius) around the putative hybrid, we noted the presence of C. cristatella Britton, C. intumescens, C. lupulina, C. pseudocyperus, C. tenera, and C. retrorsa, while only three sedges were present in an area of 78.5 m 2 (5 m radius) i.e., C. intumescens, C. lupulina and C. pseudocyperus. Two huge clumps of the putative hybrid, in full bloom, had established themselves in mud exposed to direct sunlight (Fig. 1); they were spread over an area of 90 cm by 80 cm and 110 cm by 70 cm, respectively. Clumps of other sedges found in the swamp were smaller, suggesting that the putative hybrid might imply a larger and not inventoried species. No achene was found on the in situ specimens or those collected. In the laboratory, the test of pollen colorability with cotton blue was 0%. Grains and their walls were deformed. Anthers were not exserted in the staminate spikes, or the staminate portions of the androgynous spikes. When we returned to the site in October, all infructescences of the two clumps were aborted, whereas achenes were well-developed on the surrounding sedges. Figure 1. One of the huge clumps of the putative sedge hybrid found in full bloom in an open swamp at the Bois-de-Saraguay Nature-Park (southern Québec), on July 14, 2011. Bergeron and Pellerin: Carex cayouettei, intersectional hybrid 5 Examination of 9 triplets using ordinations showed that the first PCoA axes explained the greatest amount of variance (55.8% to 84.2%), which usually located the putative hybrid in the middle of the diagrams. The second axes mostly showed the distinct nature of the putative hybrid by positioning it at one end, and the various putative parents at the other end. Comparison of 9 triplets (Fig. 2) revealed that the com hyb lup combination explained the most variance, and this combination placed the two species practically equidistant from the putative hybrid on PCoA axis I. Figure 2. Results of the nine PCoAs performed on the species-by-character tables, rescaled into Gower's dissimilarity matrices and weighted by the F-ratios. The upper part of diagram shows the scores (horizontal bar) obtained for each of the nine PCoA axis I, while the lower part shows the scores for each of the PCoA axis II. The putative hybrid (hyb) was located at zero coordinates. The explained variance (%) per axis and for each triplet analysis is shown. The species codes correspond to the first three letters of their specific epithets. Bergeron and Pellerin: Carex cayouettei, intersectional hybrid 6 The proxies of sterility (i.e., uncolored grains, undeployed anthers, aborted infructescences) and the set of intermediate characters in the PCoAs confirmed that the taxon was an intersectional hybrid between one smaller Lupulinae parent, and one large Vesicariae parent. The triplet analyses revealed that the correct hybrid combination (most equidistant position) was Carex comosa lupulina. Carex pseudocyperus is not involved in the combination, although it was observed a few meters from the hybrid. In fact, visual examination of specimens from the Montréal region (Marie- Victorin Herbarium, MT) showed us that the blade widths of the hybrid (ca mm) were consistent with the morphometry of C. comosa (sometimes 13 mm) but not with that of C. pseudocyperus (always 13 mm). Qualitatively, the broad base of the culm of the hybrid is very similar to that of C. comosa in regard to width, texture, and color. Fernald (1950) as well as Cayouette and Catling (1992) have mentioned the combination C. comosa lupulina, but there is currently no binomial name. Difficulties encountered in identification may have limited documentation, but it is possible that this taxon is more widespread than suggested by previous knowledge. To help in identification, we provide the morphological description below. Some additional measurements were taken on type specimens. Carex cayouettei A. Bergeron, hybr. nov. Figures 1, 3, 4. TYPE: CANADA. Québec. Ville de Montréal: Bois-de-Saraguay dans un marais eutrophe, me, mn (UTM 18T, NAD 83), 14 Jul 2011, A. Bergeron, M. Charrier, J.-S. Mignot, & E. Bergeron (holotype: MT; isotype: MICH); 7 Jul 2011, SP069 (paratype: DAO). Plants cespitose. Culms cm, scabrous distally. Leaves: basal sheaths brownish; blades mid to dark green, flat to W-shaped, 6 17( 19) mm wide. Inflorescences: peduncles of proximal spikes cm, scabrous distally; proximal bract cm, much longer than inflorescence, blades 6 11 mm wide, glabrous. Spikes: lateral 1 3 spikes androgynous, or pistillate, ascending to arching, flowered, cylindrical, mm; terminal 1 2( 3) spikes staminate, the proximal (if present) often ± forked and androgynous (but few perigynia at the base), mm. Staminate scales scabrous-margined. Pistillate scales narrowly lanceolate, mm, green center with subciliate hyaline margins, sometimes brown colored, apex scabrous-awned. Perigynia ascending to spreading, strongly veined, slightly stipitate, lanceovoid, inflated, trigonous to subcircular in cross section, mm; beak, 4 6 mm, bidentate; teeth, fairly straight, mm. Stigmas 3. Achenes aborted. The taxon is named in honor of the Québec botanist Jacques Cayouette, who has devoted his life to studying graminoid plants and, in particular, sedge hybrids. Distinguishing characteristics Among its congeners, Carex cayouettei is placed in sedges with culms and blades reaching a large size; with several spikes per culm having flowers either unisexuals or bisexuals, and bearing perigynia with a glabrous body and 3 stigmas. The pale brown basal sheaths and awned pistillate scales make this nothospecies similar to C. comosa from which it differs by its straight and shorter teeth of the perigynium; these latter characters are instead similar to C. lupulina. Macromorphological characters with an intermediate state relative to both parents are mainly related to the width and length of the perigynia and their beaks as well as the orientation of the perigynia along the axes of the pistillate spikes (Table 2). Some lateral (or even terminal) spikes of C. cayouettei are androgynous, which is sometimes observed in C. comosa (Hipp 2008). Similarly, the sedge hybrid most frequently bears 2( 3) terminal spikes, which is also sometimes observed in C. lupulina (but rarely according to Mohlenbrock 2011). Thus, an interesting feature of C. cayouettei is that it expresses sexual traits only occasionally encountered in both parents. Bergeron and Pellerin: Carex cayouettei, intersectional hybrid 7 Table 2. The most distinguishing characteristics of Carex cayouettei relative to its parents (C. comosa and C. lupulina). See Table 1 for data sources. Characters C. comosa C. cayouettei C. lupulina Color of basal sheath Brownish Brownish Reddish to brownish Apex of pistillate scale Awned Awned Acute to awned Shape of beak teeth Very outcurved Straight Straight Length of perigynium teeth mm mm mm Length of perigynium beak mm 4 6 mm 6 10 mm Perigynium length mm 8 11 mm mm Perigynium width mm mm 3 6 mm Orientation of perigynium Spreading to reflexed Ascending to spreading Ascending Figure 3. Illustration of Carex cayouettei showing (a) the inflorescence with terminal staminate spikes and lateral androgynous and pistillate spikes (b) the perigynium, and (c) the pistillate scale Figure 4. Holotype of Carex cayouettei A. Bergeron. Bergeron and Pellerin: Carex cayouettei, intersectional hybrid 8 Bergeron and Pellerin: Carex cayouettei, intersectional hybrid 9 Carex cayouettei is likely a true sterile hybrid with parents, C. comosa (n = 32) and C. lupulina (n = 28 30), having sets of chromosomes of a slightly different count (Wahl 1940; Reznicek & Ball 1974). This suggests that the genome of C. cayouettei contains irregular meiotic chromosome associations contributing to its complete sterility, as is observed in hybrids of different sections (Cayouette & Catling 1992; Hipp et al. 2009) although some taxa of this kind (e.g., C. langeana Fernald) can produce achenes in rare circumstances (J. Cayouette, pers. comm.). Further research is needed to verify this point. The sterility of intersectional hybrid sedges acts as a barrier to dispersal of these taxa, which explains their sporadic distribution. Thus, the presence of C. cayouettei individuals in a given place requires a hybridization event. The likelihood of the occurrence of such events may be more common than suggested by previous knowledge. First, there is a time window, from late-spring until mid-summer
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