{{Short description|Species of flowering plant}} {{Use New Zealand English|date=July 2023}} {{Use dmy dates|date=July 2023}} {{Speciesbox | image = SP100473 Myosotis arnoldii L.B.Moore WELT Te Papa 1365136 501430.jpg | image_caption = Herbarium specimen of ''Myosotis arnoldii'' plant collected in 2013 WELT SP100473 | status = NU | status_system = NZTCS | status_ref = <ref name="NZTCS"/> | genus = Myosotis | species = arnoldii | authority = [[Lucy Moore (botanist)|L.B.Moore]]<ref name=":2" /> | }}

'''''Myosotis arnoldii''''' is a species of [[flowering plant]] in the [[Family (taxonomy)|family]] [[Boraginaceae]], [[Endemic species|endemic]] to the [[South Island]] of [[New Zealand]]. [[Lucy Moore (botanist)|Lucy Moore]] described the species in 1961. Plants of this species of [[Forget-me-nots|forget-me-not]] are [[Perennial plant|perennial]] rosettes with ebracteate inflorescences, corollas ranging from yellow to dark purple, and stamens that are wholly exserted.

== Description == ''Myosotis arnoldii'' plants are rosettes. The rosette leaves have broad [[Petiole (botany)|petioles]] that difficult to distinguish from the leaf blades. The rosette leaves are 30–70&nbsp;mm long by 5–9&nbsp;mm wide (length: width ratio ca. 3–7: 1), linear-spathulate or oblanceolate, and widest at or above the middle, with an [[Acute (botany)|subacute]] to [[Obtuse (leaf)|obtuse]] apex. Both surfaces of the leaf are uniformly and densely covered in straight, appressed, white hairs that completely cover the underlying leaf surface'''.''' Each rosette has several erect, ebracteate [[inflorescence]]s that are up to 180&nbsp;mm long. The cauline leaves are similar to the rosette leaves, but smaller, are narrow-oblong and subacute, and have hairs similar to the rosette leaves.

The flowers are many per inflorescence, and each is borne on a short [[Pedicel (botany)|pedicel]], each with a bract. The calyx is c. 8&nbsp;mm long at flowering and fruiting, lobed to one-half of its length, and densely covered in straight, appressed antrorse hairs, as well as some erect hooked hairs near the base. The corolla is yellow to dark purple, "deeply coloured", and about 8–10&nbsp;mm in diameter, with a cylindrical tube, and small scales alternating with the petals. The anthers are exserted with the anthers surpassing the faucal scales. The nutlets were not described.<ref name=":0" /> Flowering occurs between October and January and fruiting from December to May.<ref name=":0" />

== Taxonomy == ''Myosotis arnoldii'' is in the plant family [[Boraginaceae]] and was originally described in 1961 by [[Lucy Moore (botanist)|Lucy Moore]] in the ''Flora of New Zealand''.<ref name=":2">{{Cite web |last=Moore |first=L.B. |title=Boraginaceae. In 'Flora of New Zealand'. (Ed. HH Allan) Vol. 1, pp. 806–833 |url=https://floraseries.landcareresearch.co.nz/pages/Taxon.aspx?id=_2dd90ab4-331f-4d49-bb31-b0a843e65931&fileName=Flora%201.xml |access-date=2022-04-27 |website=(Government Printer: Wellington, New Zealand) floraseries.landcareresearch.co.nz}}</ref><ref name=":0">{{Cite web |title=Myosotis arnoldii |url=https://www.nzpcn.org.nz/flora/species/myosotis-arnoldii/ |access-date=2023-07-26 |website=New Zealand Plant Conservation Network |language=en}}</ref>

The original specimens ([[Isotype (biology)|isotypes]]) of this species were collected by [[Arnold Wall]] from "Ben More, Ure River, [[Marlborough District|Marlborough]]", South Island, New Zealand.<ref name=":2" /> The specimens collected by Wall are housed are lodged at the [[Museum of New Zealand Te Papa Tongarewa]], Wellington (herbarium WELT).<ref name=":2" /><ref>{{Cite web |title=Myosotis arnoldii isotype {{!}} Collections Online - Museum of New Zealand Te Papa Tongarewa |url=https://collections.tepapa.govt.nz/object/664561 |access-date=2023-07-26 |website=collections.tepapa.govt.nz}}</ref><ref>{{Cite web |title=Myosotis arnoldii isotype {{!}} Collections Online - Museum of New Zealand Te Papa Tongarewa |url=https://collections.tepapa.govt.nz/object/696411 |access-date=2023-07-27 |website=collections.tepapa.govt.nz}}</ref>

The specific epithet, ''arnoldii'', is named after Arnold Wall (1869 – 1966), a New Zealand botanist who made the first collections.<ref name=":2" />

Lucy Moore suggested that ''Myosotis arnoldii'' is morphologically most similar to ''[[Myosotis angustata|M. angustata]]'' and ''[[Myosotis macrantha|M. macrantha]]'' based on habit and leaves, and to ''[[Myosotis albosericea|M. albosericea]]'' based on the very dense covering of white, appressed hairs on its vegetative parts including the rosette and stem leaves, which completely obscure the epidermis.<ref name=":2" /> These hairs are antrorse (forward facing), straight, and on the leaf are oriented parallel to the midrib. The only other New Zealand species with such hairs is ''Myosotis albosericea,'' [[Endemism|endemic]] to southern South Island, New Zealand.<ref name=":13">{{Cite journal |last=Meudt |first=Heidi |date=2021 |title=Taxonomic revision of five species groups of ebracteate-erect Myosotis (Boraginaceae) endemic to New Zealand, based on morphology, and description of new subspecies |url=https://www.publish.csiro.au/SB/SB20028 |journal=Australian Systematic Botany |volume=34 |issue=3 |pages=252–304 |doi=10.1071/SB20028 |s2cid=234771910|url-access=subscription }}</ref>

=== Phylogeny === No individuals of ''M. arnoldii'' were included in [[Phylogenetics|phylogenetic]] analyses of standard DNA sequencing markers ([[Ribosomal DNA|nuclear ribosomal DNA]] and [[chloroplast DNA]] regions) of New Zealand ''Myosotis.<ref name=":12">{{Cite journal |last1=Meudt |first1=Heidi M. |last2=Prebble |first2=Jessica M. |last3=Lehnebach |first3=Carlos A. |date=2015-05-01 |title=Native New Zealand forget-me-nots (Myosotis, Boraginaceae) comprise a Pleistocene species radiation with very low genetic divergence |url=https://doi.org/10.1007/s00606-014-1166-x |journal=Plant Systematics and Evolution |language=en |volume=301 |issue=5 |pages=1455–1471 |doi=10.1007/s00606-014-1166-x |issn=2199-6881 |s2cid=254048318|url-access=subscription }}</ref><ref name=":32">{{Cite journal |last1=Winkworth |first1=Richard C |last2=Grau |first2=Jürke |last3=Robertson |first3=Alastair W |last4=Lockhart |first4=Peter J |date=2002-08-01 |title=The origins and evolution of the genus Myosotis L. (Boraginaceae) |url=https://www.sciencedirect.com/science/article/pii/S1055790302002105 |journal=Molecular Phylogenetics and Evolution |language=en |volume=24 |issue=2 |pages=180–193 |doi=10.1016/S1055-7903(02)00210-5 |issn=1055-7903 |pmid=12144755|url-access=subscription }}</ref>'' In those studies, within the southern hemisphere lineage, species relationships were not well resolved.<ref name=":12" /><ref name=":32" />

Three individuals from one population of ''M. arnoldii'' were also genotyped in a study that developed microsatellite DNA markers for another species group of New Zealand ''Myosotis.''<ref>{{Cite journal |last=Prebble |first=Jessica |last2=Tate |first2=Jennifer Alane |last3=Meudt |first3=Heidi |last4=Symonds |first4=Vaughan |date=2015-06-09 |title=Microsatellite markers for the New Zealand endemic Myosotis pygmaea species group (Boraginaceae) amplify across species |url=https://bsapubs.onlinelibrary.wiley.com/doi/full/10.3732/apps.1500027 |journal=Applications in Plant Sciences |volume=3 |issue=6 |doi=10.3732/APPS.1500027 |pmc=4467761 |pmid=26082880}}</ref><ref name=":02">{{Cite journal |last=Prebble |first=Jessica |last2=Meudt |first2=Heidi |last3=Tate |first3=Jennifer Alane |last4=Symonds |first4=Vaughan |date=2019-08-01 |title=Comparing and co‐analysing microsatellite and morphological data for species delimitation in the New Zealand native Myosotis pygmaea species group (Boraginaceae) |url=https://onlinelibrary.wiley.com/doi/10.1002/tax.12096 |journal=Taxon |language=English |volume=68 |issue=4 |pages=731–750 |doi=10.1002/TAX.12096|url-access=subscription }}</ref> The individuals of ''M. arnoldii'' included showed a high number of alleles that cross-amplified at most of the microsatellite loci.<ref name=":02" />

== Distribution and habitat == ''Myosotis'' ''arnoldii'' is a [[forget-me-not]] is known to occur in two disjunct populations in the northern part of the South Island, New Zealand.<ref name=":0" /><ref name=":1">{{Cite thesis |last=Mary Brandon |first=Andrea |title=Breeding systems and rarity in New Zealand Myosotis |date=2001 |degree=PhD |publisher=[[Massey University]] |url=http://hdl.handle.net/10179/2146}}</ref> This species grows on cliff faces and other rocky habitats on marble substrates on Hoary Head, North West Nelson and on limestone substrates at its type locality in the Chalk Range, Marlborough.<ref name=":0" /><ref name=":2" /><ref>{{Cite web |title=Calcareous cliffs, scarps and tors |url=https://www.landcareresearch.co.nz/publications/naturally-uncommon-ecosystems/inland-and-alpine/calcareous-cliffs-scarps-and-tors/ |access-date=2023-07-26 |website=Manaaki Whenua |language=en-US}}</ref>

''Myosotis arnoldii'' is likely to be an outcrossing species, with plants requiring a pollinating vector to achieve pollination and seed set.<ref name=":1" />

== Conservation status == ''Myosotis arnoldii'' is listed as At Risk – Naturally Uncommon with the qualifiers Data Poor (DP) and Range Restricted (RR) on the most recent assessment (2017–2018) under the [[New Zealand Threat Classification System|New Zealand Threatened Classification]] system for plants.<ref name="NZTCS">{{Cite journal |last1=Lange |first1=Peter J. de |last2=Rolfe |first2=Jeremy R. |last3=Barkla |first3=John W. |last4=Courtney |first4=Shannel P. |last5=Champion |first5=Paul D. |last6=Perrie |first6=Leon R. |last7=Beadel |first7=Sarah M. |last8=Ford |first8=Kerry A. |last9=Breitwieser |first9=Ilse |last10=Schönberger |first10=Ines |last11=Hindmarsh-Walls |first11=Rowan |date=May 2018 |title=Conservation status of New Zealand indigenous vascular plants, 2017 |url=https://www.doc.govt.nz/globalassets/documents/science-and-technical/nztcs22entire.pdf |journal=New Zealand Threat Classification Series |volume=22 |pages=45 |oclc=1041649797}}</ref>

== References == {{Reflist}}

== External links == {{Commons}} * [https://avh.ala.org.au/occurrences/search?taxa=myosotis+arnoldii#tab_mapView ''Myosotis arnoldii'' occurrence data from Australasian Virtual Herbarium]

{{Taxonbar|from=Q17416594}}

[[Category:Myosotis|arnoldii]] [[Category:Endemic flora of New Zealand]] [[Category:Endangered flora of New Zealand]] [[Category:Plants described in 1961]] [[Category:Flora of the South Island]]