Myosotis brevis de Lange & Barkla

Prebble, Jessica M., Symonds, V. Vaughan, Tate, Jennifer A. & Meudt, Heidi M., 2022, Taxonomic revision of the southern hemisphere pygmy forget-me-not group (Myosotis; Boraginaceae) based on morphological, population genetic and climate-edaphic niche modelling data, Australian Systematic Botany 35 (1), pp. 63-94 : 79-81

Myosotis brevis de Lange & Barkla in P. J. de Lange et al. Threat. Pl. New Zealand 437 (2010)

[nom. nov., non M. minutiflora Boiss. & Reut., Pugill. Pl. Afr. Bor. Hispan. 80 (1852)]

Myosotis pygmaea var. minutiflora G.Simpson & J.S.Thomson, Trans. & Proc. Roy. Soc. New Zealand 73: 161 (1943) Type citation: ‘habitat: moist ground at lake shores. Type specimen from Lake Lyndon , in the herbarium, Plant Research Bureau, Wellington.’ Type: NEW ZEALAND. Canterbury. Lake Lyndon, moist ground at lake shores, s. dat., G. Simpson & J. S. Thomson s.n. (holo: CHR 75725 !) .

Myosotis pygmaea var. imbricata Cockayne, Veg. New Zealand 2nd edn, 396 (1928), nom. nud.

Description

Rosette plants with multiple prostrate branches up to 5 cm long. Rosette leaves 1–9; petioles (0–)0.7–7.0 mm long; lamina usually flat, oblanceolate to broadly obovate, 1–9 mm long, 0.9–4 mm wide (length:width ratio 1.2–2.5:1), green to brown; apex obtuse (or occasionally acute), with hydathode on abaxial side; trichomes densely distributed and often overlapping, flexuous, antrorse, appressed to erect, spreading or sometimes appressed on leaf margins, distributed evenly (on leaf adaxial surface), but sparsely distributed, or on leaf midribs only, or absent (on leaf abaxial surface), (0.2–)0.4–0.9(–1.6) 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 2.7 mm; distal cauline leaves subtending flowers up to 17 per branch, lamina 1.0– 6.5 mm long, 0.5–2.3 mm wide, usually sessile. Pedicels up to 0.7 mm long (flowering) or 0.8 mm long (fruiting). Calyx 0.7–1.7 mm long (flowering), increasing to 1.7–3.7 mm long (fruiting), 0.9–3.2 mm wide at the top at fruiting, lobed to 1/3–2/3 the length of the calyx; with trichomes usually of uniform length, denser along calyx ribs, occasionally of two different lengths, longer and antrorse on ribs v. shorter and retrorse between ribs and near the base. Corolla 0.5–1.5(–2.0) mm in diameter, white or cream, occasionally pale blue or cream striped with blue; faucal scales yellow; corolla lobes 0.2–0.5(–0.7) mm long, 0.2–0.4(–0.7) mm wide; corolla tube 0.3–0.5(–0.9) mm wide at faucal scales, 0.8–1.6 mm long from base to faucal scales, narrow cylindric. Stamens 5, included; filaments attached below faucal scales, filaments 0–0.1 mm long; anthers 0.2–0.3(–0.5) mm long, subsessile. Style 0.5–1.2 mm long (flowering) to 0.5–1.6(–2) mm long (fruiting). Nutlets 4, 0.9–1.2(–1.4) mm long, 0.5–0.8 mm wide.

Illustration citations

Fig. 4 ; Webb and Simpson (2001, p. 142), as M. pygmaea var. minutiflora ; de Lange et al. (2010, pp. 300–301).

Distribution

NEW ZEALAND: North Island: Taranaki, Southern North Island; South Island : Canterbury and Otago ( Fig. 4 ).

Habitats

North Island, Southern North Island: shore platforms, clifftop herb fields and turfs, or beach gravels. South Island, Canterbury: in shingle or mud at seasonally inundated lake or tarn edges; Otago: dry, exposed, sunny, sometimes seasonally moist, alpine fell field, cushion field, eroded pasture, or turf. Elevation sea level to 1900 m.

Phenology

Flowering September–April. Fruiting October–April. Peak flowering and fruiting October–December.

Notes

Identification. Myosotis brevis is the smallest New Zealand forget-me-not. Plants of this species can be distinguished from all other Myosotis , including other pygmy forget-me-nots, on the basis of their smaller corolla diameter of 0.5–1.5(–2.0) mm, smaller calyx length at flowering of 0.7–1.7 mm and smaller nutlet size of 0.9–1.2(–1.4) mm long, 0.5–0.8 mm wide. When not in flower or fruit, plants of M. brevis can be difficult to distinguish from small plants of M. antarctica subsp. antarctica , because plants of both species have flexuous trichomes. However, plants of M. brevis are usually spring annuals (Rogers et al. 2002, as M. pygmaea var. minutiflora ; de Lange et al. 2010), and it is rare to find plants that are not in either flower or fruit.

Taxonomic history. Myosotis brevis was first described as a variety of M. pygmaea (as var. minutiflora ; Simpson and Thomson 1943). It was then elevated to species rank on the basis of its morphological distinctiveness ( de Lange et al. 2010) and because the name M. minutiflora was already in use for a species with a European type, the replacement name of M. brevis was chosen. Species rank is considered to be appropriate for this taxon, given the multiple discrete morphological characters and molecular evidence that unites it (see below).

Patterns in the data. Myosotis brevis specimens can be distinguished both morphologically ( Prebble et al. 2018) and genetically ( Prebble et al. 2019). In an nMDS analyses of morphological characters measured on herbarium specimens, all samples of M. brevis group together (fig. 6A in Prebble et al. 2018). Multiple morphological characters were found to significantly distinguish M. brevis from other pygmy forget-me-not species in both the herbarium and growth-room datasets, for example, length of calyx at fruiting, floral lobe length and nutlet length. When molecular data from microsatellites was integrated with the morphological data from herbarium specimens, all populations identified as M. brevis formed a significantly differentiated cluster (fig. 6 in Prebble et al. 2019). When analysing just the molecular data, all M. brevis populations fall into a single cluster in the Structure analyses of K = 3 (fig. 3 in Prebble et al. 2019), and most populations of M. brevis form a group in the NeighbourNet network (fig. 5 in Prebble et al. 2019).

However, plants from three locations not identified as Myosotis brevis also grouped genetically with M. brevis in the Structure analyses of K = 3, including three populations of M. antarctica subsp. traillii from one area (North Island, Southern North Island: WELT SP090629, WELT SP090631 and WELT SP090634) and three populations of M. antarctica subsp. antarctica from two locations (South Island, Canterbury, Lake Tennyson: WELT SP100425; Campbell Island, Mt Honey: WELT SP102779 and WELT SP102780). Five of the six populations (the three populations of M. antarctica subsp. traillii and two populations of M. antarctica subsp. antarctica from Campbell Island) are likely to group with M. brevis because of an artefact of the analyses. Specifically, these five populations, together with populations of M. brevis , all have high numbers of unique alleles and allelic diversity (see scored microsatellite data in Prebble et al. 2020). In the Structure analysis of this dataset at K = 3, in which three groups must be recovered, these five populations and the populations of M. brevis cluster together on the basis of this, thus forming the group at K = 3 with the highest number of unique alleles and highest allelic diversity. Put another way, these five populations cluster together and with M. brevis because they are the most different from one another and from all other sampled populations, rather than because they are most similar to each other or to M. brevis . For the remaining population (from Lake Tennyson, Canterbury WELT SP100425) there may be a different explanation, because this specimen was identified by J. M. Prebble as M. antarctica subsp. antarctica (not M. brevis ) only because of nutlet size (1.4 × 1.0 mm v. the range for M. brevis nutlets of 0.9–1.2 × 0.5–0.8 mm; flowers absent). However, given that it shares a habitat and morphology otherwise similar to M. brevis , and plants at this location have been identified as M. brevis previously (Rogers et al. 2002), this is a difficult population to classify. Nevertheless, when microsatellite and morphological data were co-analysed, this population did not group with M. brevis (fig. 6 in Prebble et al. 2019) and, on that basis, we identify this population as M. antarctica subsp. antarctica here.

Pollen morphology. Pollen of Myosotis brevis has the M. discolor morphology type, and although it fell into Cluster 1 in an nMDS analyses with other pollen identified as the M. australis type (see fig. 2 in Meudt 2016), its pollen is nevertheless the most distinctive of all bracteate-prostate species ( Meudt 2016). This pollen morphology type was previously not known from New Zealand Myosotis and was hypothesised to represent parallel evolution owing to a shared annual habit between M. brevis and other Myosotis species with the M. discolor pollen type. Some individuals of M. australis and M. saxatilis have also been found to have this pollen type ( Meudt et al. 2020).

Chromosome number. Unknown.

Recommended conservation status

Previously, Myosotis brevis was assessed as Threatened – Nationally Vulnerable C(3) with the qualifiers Extreme Fluctuations and Sparse ( de Lange et al. 2018). Of all the pygmy forget-me-nots, Myosotis brevis was found to have the largest estimated census size (17 600), even though it had the smallest number of populations (35) ( Table 6 ). Myosotis brevis has a large enough census size that it could be considered At Risk – Naturally Uncommon; however, its small area of occupancy ( Table 6 ) and fluctuating population size (Rogers et al. 2002) mean that it is better placed in the Threatened, Naturally Vulnerable category (see Table 6 for details). Therefore, we recommend leaving the current conservation status and qualifiers unchanged from those of de Lange et al. (2018).

Threats. The main threats to Myosotis brevis are habitat loss, and invasive weeds leading to overshading ( de Lange et al. 2010). North Island populations of M. brevis are more at risk than the South Island populations. The North Island populations are smaller on average (190 v. 1000 plants per population) and cover a smaller area on average (34 × 34 m v. 83 × 83 m). The M. brevis bare pavement habitat in Otago may be increasing (Rogers et al. 2002), whereas the coastal habitat in the North Island is at risk; for example, populations around Taranaki (WELT SP090361), Wairarapa (WELT SP090545) and Wellington (WELT SP090550) grow in habitat types that are themselves considered acutely threatened ( Department of Conservation 2014). Furthermore, none of the North Island populations inhabits DOC-managed land (Supplementary Table S1 ). The populations around the North Island Taranaki coast appear particularly precarious; for example, the population visited at Puketapu Road (WELT SP090361) is less than 2 m from the edge of an eroding cliff, but the population cannot migrate inland because of farmland (J. M. Prebble, pers. obs., 2011). At least one population that has recently (c. 2005) gone extinct in the East Cape was most likely to be M. brevis ; its habitat is thought to have been destroyed by wild goats (G. Atkins, pers. comm. 2012). The two most genetically distinct M. brevis populations are one from the North Island (Taranaki, St Road; WELT SP090543) and one from the South Island (Otago, Bendigo; WELT SP102760); these could be prioritised when it comes to potential conservation effort.

Representative specimens (58 specimens examined)

NEW ZEALAND. North Island : Taranaki: Puketapu Rd end , Nov. 1971, A. P. Druce s.n. ( CHR 245911 ); Stent Rd , 5 Oct. 2011, H. M. Meudt HMM311, J. M. Prebble, C. Ogle, E. King, K. Eaton, G. La Cock, B. Clarkson, M. Parsons & B. Hartley ( WELT SP090543 ). Southern North Island : Kawakawa Rocks , near Ngawi, 1 Nov. 2011, H. M. Meudt HMM313, J. M. Prebble, B. Sneddon & T. Silbery ( WELT SP090545/A ); Te Ikaamaru Bay , 7 Nov. 2011, H. M. Meudt HMM317, J. M. Prebble, P. Garnock-Jones & E. Robertson ( WELT SP090549 ); Te Ohau Bay , 7 Nov. 2011, H. M. Meudt HMM318, J. M. Prebble, P. Garnock-Jones & E. Robertson ( WELT SP090550/A ). South Island : Canterbury, Lake Lyndon ; 21 Feb. 2012, J. M. Prebble JMP12009 & M. Thorsen ( WELT SP093294 ); Lake Lyndon , Nov. 1971, A. P. Druce s.n. ( CHR 208536 ). Otago: Bannockburn , 8 Oct. 2013, J. M. Prebble JMP13045 ( WELT SP102761 ); Bendigo , 8 Oct. 2013, J. M. Prebble JMP13044 ( WELT SP102760 ); Chapman Rd Reserve , 9 Oct. 2013, J. M. Prebble JMP13046 ( WELT SP102762 ); Hawkdun Range , 8 Dec. 2011, J. Barkla s.n. ( WELT SP093498 ); Nevis Valley , Feb. 1992, A. P. Druce s.n. ( CHR 476031 ); Springvale Reserve , 9 Oct. 2013, J. M. Prebble JMP13047 ( WELT SP102763 ) .

Figures

Fig. 4. Myosotis brevis photographs and distribution map. (a) Habit. (b) Inflorescence showing cauline leaf abaxial side. (c) Inflorescence showing cauline leaf adaxial side, calyces, and flower. (d) Rosette leaf adaxial side showing colour morphs. (e) Flower. (f) Nutlet. (g) Map of georeferenced herbarium specimens observed by J. M. Prebble (25). White scale bars: 2 mm; black scale bar: 1 mm. Photo credits: a–e © Te Papa by H. M. Meudt (a: WELT SP090549, Te Ikaamaru Bay, Wellington; b, c: WELT SP090545, Ngawi, Wairarapa; d: WELT SP090543, Stent Road, Taranaki; e: WELT SP090550, Ohau Bay, Wellington); f by J. M. Prebble (WELT SP090543, cultivated ex Stent Road, Taranaki).