Taxonomic revision of the southern hemisphere pygmy forget-me-not group (Myosotis; Boraginaceae) based on morphological, population genetic and climate-edaphic niche modelling data Author Prebble, Jessica M. Author Symonds, V. Vaughan Author Tate, Jennifer A. Author Meudt, Heidi M. text Australian Systematic Botany 2022 2022-05-05 35 1 63 94 http://dx.doi.org/10.1071/sb21031 journal article 10.1071/SB21031 1446-5701 10903921 Myosotis glauca (G.Simpson & J.S.Thomson) de Lange & Barkla in P. J. de Lange et al . Threat. Pl. New Zealand 438 (2010) Myosotis pygmaea var. glauca G.Simpson & J.S.Thomson, Trans. & Proc. Roy. Soc. New Zealand 72: 26 (1942) . Type citation : ‘ Habitat : Grassland at Mount Ida. Type specimens from the base of Mount Ida at 500 m . altitude, in the Herbarium, Plant Research Bureau, Wellington .’ Type : NEW ZEALAND : Otago . Base of Mt Ida at 500 m , grassland, s. dat ., Simpson & Thomson s.n. ( lecto [designated by L. B. Moore in H. H. Allan (Ed.), Fl. New Zealand 1: 816 (1961) ]: CHR 75722 !; isolecto : AK 210591 !) . Typification notes The type citation mentions ‘ specimens ’ plural, but there is only one specimen at CHR (formerly BD) that matches the type citation, CHR 75722. However, AK 210591 has identical collection information. The AK specimen is considered to be a duplicate of the CHR specimen ( E. Cameron , Auckland Museum , pers. comm.), so we can assume that it was once held at CHR and subsequently sent to AK, making this an isolectotype . Description Rosette plants with multiple prostrate branches up to 12 cm long. Rosette leaves 4–15; petioles 1.5–9.0 mm long; lamina usually flat, narrowly oblanceolate to broadly obovate, 3.7–17.0 mm long 1.5–7.0 mm wide (length:width ratio 1.3–3.5:1), dull greyish-green (glaucous) or occasionally bright green; apex obtuse, with hydathode on abaxial side; trichomes sparsely distributed, straight, antrorse, appressed to patent, appressed on margins, distributed evenly (on adaxial surface), and usually absent or occasionally sparsely distributed and on midrib (of abaxial surface), (0.2–)0.4–0.8(–1.2) mm long, deciduous with age. Basal cauline leaves not subtending flowers, 1–5 per branch, lamina similar in size and shape to the rosette leaves, with petioles up to 7.5 mm ; distal cauline leaves subtending flowers up to 19 per branch, lamina 2.0– 11.5 mm long, 1.0–5.0 mm wide, usually sessile. Pedicels up to 1.0 mm long (flowering) or 1.8 mm long (fruiting). Calyx 1.6–3.3 mm long (flowering) increasing to 2.5–7.8 mm long (fruiting), 1.3–4.3 mm wide at the top at fruiting, lobed to 1/4–1/2 the length of the calyx, with trichomes usually only along ribs both inside and outside the calyx, but occasionally present in between ribs. Corolla (1.0–)1.4–4.0 mm in diameter, white; faucal scales yellow; corolla lobes 0.3–1.3 mm long 0.2–1.0 mm wide; corolla tube 0.4–1.1 mm wide at faucal scales, 1.2–2.5(–3.2) mm long from base to faucal scales, narrow cylindric. Stamens 5, included; filaments attached below faucal scales, 0.0– 0.1 mm long; anthers 0.4–0.9 mm long, subsessile; style 0.8–2.3 mm long (flowering) to 0.9–2.8 mm long (fruiting). Nutlets 4, (1.0–) 1.2–1.5 mm long, (0.7–) 0.8–1.2 mm wide. Illustration citations Fig. 5 ; Moore (1961 , p. 808), as M. pygmaea var. glauca ; Webb and Simpson (2001 , p. 142), as M. pygmaea var. glauca ; de Lange et al . (2010 , pp. 404–405); Mark (2012 , p. 257). Distribution NEW ZEALAND : South Island : Canterbury and Otago ( Fig. 5 ). Habitats Fine semi-consolidated gravels on lake, tarn or stream edges, erosion fans, the base of tors, or old mine tailings. Depleted tussock-grassland, low grass turf. Elevation 180–1500 m . Phenology Flowering September–March. Fruiting October–April. Peak flowering and fruiting December–January. Fig. 5. Myosotis glauca photographs and distribution map. ( a ) Habit. ( b ) Rosette leaves, adaxial and abaxial sides. ( c ) Calyces, left to right most to least mature. ( d ) Nutlets. ( e ) Map of georeferenced herbarium specimens observed by J. M. Prebble (16). White scale bars: 2 mm; black scale bar: 1 mm. Photo credits: all by J. M. Prebble (WELT SP093285, Nevis Valley, Otago). Notes Identification . Myosotis glauca plants can be distinguished from other pygmy forget-me-nots by their straight, appressed, non-overlapping trichomes and (usually) glaucous grey leaves. M. glauca as here circumscribed is known only from Central Otago and southern Canterbury . Specimens identified as M. glauca collected from the North Island Central Plateau previously identified as M. glauca (e.g. CHR 252337) do not solely have the straight, appressed leaf trichomes that characterise all other plants that fall under this species. Instead, a small number of straight, appressed trichomes are mixed with flexuous, patent trichomes, and therefore these specimens are better included in M. antarctica subsp. antarctica . Although most plants of M. glauca have glaucous green to grey leaves, some plants with brighter green leaves from the Pisa Range (previously identified as M. aff. glauca , e.g. WELT SP089898) cannot be distinguished from the remainder of M. glauca . Leaf colour variation is known from other pygmy forget-me-nots, notably M. brevis ( Fig. 4 ), and thus these M. aff. glauca specimens are considered here to be M. glauca sens . str. , which is variable in leaf colour. Recent collections of M. aff. glauca (a) “Mata-Au” (WELT SP104520) from the Clutha outwash are difficult to place owing to their unusual combination of glaucous leaf colour with flexuous trichomes, and require further study (more details below). Taxonomic history . Myosotis glauca was first described as a variety of M. pygmaea (as var. glauca ; Simpson and Thomson 1942 ). It was then elevated to species rank owing to its morphological distinctiveness ( de Lange et al . 2010 ). Species rank is considered appropriate for this taxon, given the morphological and molecular evidence that defines it and distinguishes it from other species (see below). The morphological description given here differs subtly from that given by de Lange et al . (2010 , p. 405). Specifically, two characters they identified as distinguishing M. glauca were not found here to be diagnostic, i.e. ‘…inner calyx surface midline of M. glauca is furnished with 4–5 shortly erect, stiff hairs’, and ‘broadly ovate rather than narrowly ovate nutlets (seeds)’. The surface of the inner calyx of M. glauca specimens was found to be sometimes glabrous, sometimes covered in short stiff hairs, and sometimes as described above by de Lange et al . (2010) (data not shown). The length to width ratio of M. glauca nutlets was not found to differ from that of M. antarctica , although nutlets of M. brevis did have a slightly higher length: width ratio on average (visible in Fig. 4 v . 5 ). Patterns in the data . Specimens of Myosotis glauca are united by morphological ( Prebble et al . 2018 ) and genetic ( Prebble et al . 2019 ) data. In the nMDS analyses of morphological characters measured on herbarium specimens, all samples of M. glauca group together (fig. 6 in Prebble et al . 2018 ). Qualitative morphological characters distinguish M. glauca from all other pygmy forget-me-nots, i.e. leaf colour (usually glaucous-green to grey), and trichomes that are straight and appressed on the leaf blade and leaf margins ( Fig. 5 ). In the analyses of microsatellite data, all populations of M. glauca form a cluster in the Structure analyses above K = 10 (fig. 3 in Prebble et al . 2019 ), and these populations also group together in the NeighbourNet network (fig. 5 in Prebble et al . 2019 ). Five specimens identified as Myosotis aff. glauca (see appendix 1 in Prebble et al . 2018 ) cluster with those identified as M. glauca sens . str. on the basis of morphological data (fig. 6 in Prebble et al . 2018 ), and appear to differ only by having brighter green leaves than is usual for M. glauca . Only one individual identified as M. aff. glauca was included in the genetic dataset (WELT SP093282); so, little is known regarding genetic relationships, except that this one individual does not cluster with other M. glauca populations. Specimens identified as M. aff. glauca are therefore here considered part of M. glauca on the basis of morphological similarity. Recent collections identified as M. aff. glauca (a) “Mata-Au” (WELT SP104520), WELT SP108906 and WELT SP104520) are from a single locality from the terraces of glacial outwash gravels of the Clutha River/ Mata-Au below Lake Wanaka, Otago , and appear to possess a unique suite of character traits compared with other pygmy Myosotis , i.e. a more erect or decumbent habit, purple stems, two leaf colour morphs (glaucous grey-green or brown) and flexuous, patent to erect trichomes. They have been observed to have a spring annual life cycle like many M. brevis (Geoff Rogers, formerly of DOC, pers. comm., July 2016 ). Apart from the more erect habit, they are somewhat morphologically intermediate between M. glauca and M. antarctica subsp. antarctica or M. brevis . Measurements of a single plant (that at the time was the only material available for study) was included in the nMDS analyses of morphological characters measured on herbarium specimens, which placed this sample within the cluster containing M. antarctica subsp. antarctica + M. brevis and not M. glauca , although with high uncertainty (fig. 6 in Prebble et al . 2018 ). Four individuals were included in the microsatellite dataset, and genetically M. aff. glauca (a) “Mata-Au” (WELT SP104520) does not appear to be affiliated with M. glauca on the basis of the Structure, nMDS and NeighbourNet network of microsatellite data (figs 3–5 in Prebble et al . 2019 ), but may be similar to the single included specimen of M. aff. glauca (WELT SP093282; on the basis of the Structure and NeighbourNet but not nMDS analyses). Although we do not consider M. aff. glauca (a) “Mata-Au” (WELT SP104520) to be included within M. glauca , with only a few collections from a single location, we are not yet confident in describing this putative taxon as a species. Further research into the pollen morphology and genetic affinities would be beneficial. Pollen morphology . Pollen of Myosotis glauca has the M. australis morphology type , the most common pollen type for bracteate-prostrate Myosotis species ( Meudt 2016 ) and the ebracteate-erect species sampled so far ( Meudt et al . 2020 ). Representative specimens were recovered in both Clusters 1 and 2 in an nMDS analysis (see fig. 2. in Meudt 2016 ), along with all other pollen of the M. australis morphology type . The separation between Clusters 1 and 2 was not high, with several samples, including four of the five M. glauca specimens, having high uncertainty in their placement intermediate between the two clusters. The main morphological difference between the two clusters is that those specimens in Cluster 1 usually had eight pollen apertures, and those in Cluster 2 usually had 10 apertures, but this is not always a simple character to assign because some individuals are polymorphic for aperture number. Chromosome number . Unknown. Recommended conservation status De Lange et al . (2018) listed Myosotis glauca as Threatened – Nationally Vulnerable C(3) with the qualifiers Data Poor and Sparse . It is clear from the data that Myosotis glauca indeed fits the criteria for Threatened – Nationally Vulnerable on the basis of both census size and small areas of occupancy and should maintain that conservation status ( Table 6 ). The data qualifier Sparse should also be maintained, but the qualifier Data Poor is no longer applicable and should be replaced with Range Restricted (see Table 6 for more details). Threats . The main threat to Myosotis glauca is considered to be weed invasion ( de Lange et al . 2010 ). Myosotis glauca is the least common pygmy forget-me-not on the basis of estimated census size; it is found only in Central Otago and southern Canterbury, and only five of its populations (31%) grow on DOC-managed land ( Table 6 ). At one of those sites (Lake Ohau, AK 280800), plants of M. glauca could not be found in 2013, and further searches are recommended. Populations from two locations included in the microsatellite analysis of Prebble et al . (2019) ( Nevis valley: WELT SP093284 & WELT SP093285, and Macraes: WELT SP100497) are from areas both managed by DOC. With the decision to reject a proposal to dam the Nevis Valley (Environment Court decision, 2013, available at http://www.nzlii.org/cgi-bin/sinodisp/nz/cases/NZEnvC/ 2013/131.html?query=nevis, accessed 11 November 2020 ), the future of populations there has become more secure. Representative specimens ( 39 specimens examined) NEW ZEALAND . South Island : Canterbury : Lake Ohau , 27 Oct. 2002 , A. E. Wright 12963 ( AK 280800 ) . Otago : base of Mt Ida , s. dat. , G. Simpson & J. S. Thomson s.n. ( AK 210591 ) ; Dunstan , 17 Jan. 2006 , M. Thorsen s.n. ( WELT SP089837 ); Kyeburn Diggings , 9 Dec. 2006 , M. Thorsen s.n. ( WELT SP089838 ); Macraes flats , 1 Mar. 2013 , J. M. Prebble JMP13039 & K. Pilkington ( WELT SP100497 ); mountains of Vincent County , s. dat. , D. Petrie s.n. ( WELT SP081871 ); Nevis Valley , 25 Apr. 2004 , M. Thorsen s.n. ( WELT SP089836 ); School House Flat , Nevis Valley , 15 Feb. 2012 , J. M. Prebble JMP12003 & JMP12004 ( WELT SP093284 & WELT SP093285 ); Tourist Spur on Mt Ida , 26 Apr. 1969 , L. B. Moore s.n. ( CHR 191750 ) ; Pisa Range , around snowfarm, 23 Jan. 2006 , M. Thorsen s.n. ( WELT SP089898 ); Pisa Range , Roaring Meg , 14 Feb. 2012 , J. M. Prebble JMP12002 ( WELT SP093282 ); western Pisa Range , 26 Jan. 2006 , M. Thorsen s.n. ( CHR 586018 ) ; western slopes of The Remarkables , 25 Jan. 1972 , C. Meurk s.n. ( OTA 34535 ) .