Myosotidium
{{short description|Monotypic genus of plants in the borage family Boraginaceae}}
{{Use dmy dates|date=July 2019}}
{{Use New Zealand English|date=October 2024}}
{{speciesbox
|image = Chatham Island forget-me-nots (Myosotidium hortensia).jpg
|image_caption =
|genus = Myosotidium
|parent_authority = Hook.
|species = hortensia
|synonyms_ref = {{GRIN | Myosotis hortensia | 24811 | accessdate = 2008-07-20}}{{cite web |url= https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:118872-1 |title= Myosotidium hortensia (Decne.) Baill. |author= |date=n.d. |website=Plants of the World Online |publisher=The Trustees of the Royal Botanic Gardens, Kew |access-date=December 26, 2022}}
|synonyms = Myosotis hortensia Decne.
Cynoglossum cyaneum Hook.f.
Cynoglossum nobile Hook.f.
Myosotidium nobile (Hook.f.) Hook.
}}
Myosotidium is a genus of plants belonging to the family Boraginaceae. This genus is represented by the single species Myosotidium hortensia, the Chatham Islands lily, giant forget-me-not{{PLANTS|id=MYHO4|taxon=Myosotidium hortensia|accessdate=15 July 2015}} or Chatham Islands forget-me-not, which is endemic to the Chatham Islands, New Zealand. In the Māori language, it is known by the name kopukapuka.{{cite web |title=New Zealand Native Plants Photography - recent NZ natives additions Nov 2005 page 2 |url=http://www.nzplantpics.com/sfeature_galleries/_new_nz_native_plants/nz_native_plants_nov_05b.htm |website=www.nzplantpics.com |access-date=26 July 2021}}{{cite web |title=Kopukapuka |url=https://natlib.govt.nz/records/22623429 |website=Kopukapuka {{!}} Items {{!}} National Library of New Zealand {{!}} National Library of New Zealand |access-date=26 July 2021 |language=en}}
The biogeography is yet unresolved, but its ancestors may have originated from the American continent, as Myosotidium hortensia was found to be sister to the South American plant genus Selkirkia{{Cite journal | last1 = Holstein | first1 = N. | last2 = Chacón | first2 = J. | last3 = Hilger | first3 = H. H. | last4 = Weigend | first4 = M. | title = No longer shipwrecked—Selkirkia (Boraginaceae) back on the mainland with generic rearrangements in South American "Omphalodes" based on molecular data | doi = 10.11646/phytotaxa.270.4.1 | journal = Phytotaxa | volume = 270 | issue = 4 | pages = 231–251 | year = 2016}} and both genera being sister to the North American genus Mimophytum.{{Cite journal | last1 = Holstein | first1 = N. | last2 = Chacón | first2 = J. | last3 = Otero | first3 = A. | last4 = Jiménez-Mejías | first4 = P. | last5 = Weigend | first5 = M. | title = Towards a monophyletic Omphalodes—or an expansion of North American Mimophytum | doi = 10.11646/phytotaxa.288.2.3 | journal = Phytotaxa | volume = 288 | issue = 2 | pages = 131–144 | year = 2016}}
Myosotidium hortensia is a fleshy herb with large orbicular somewhat fleshy leaves and apparently parallel leaf venation. The inflorescence bears numerous blue flowers in the late spring. The relatively large blackish seeds are winged. It is much planted as a garden ornamental flower in New Zealand and elsewhere. In addition to the blue-flowered species, 'Alba', a white flowered cultivar is also popular in cultivation. In its natural habitat, M. hortensia occurs near beaches under the direct influence of sea-water spray and sea-winds.