Ritter F. 1980, Kakteen in Südamerika (3):1070

 

Ritter notes that the fruit is unusual for the genus by being woolly, a primitive characteristic.  He also notes that the tubercled rather than ribbed stem and the slightly felted apex can be regarded as persistent juvenile characters, which can be explained by the need for the plant to multiply as early as possible, before they fall victim to the Guanacos.

The hairy ovary and fruit are a link with Ritter's Pilocopiapoa solaris.

Taylor N. P.  1981, A commentary on Copiapoa, The Cactus and Succulent Journal of Great Britain, 43(2/3): 49-60

Taylor considers the next most northern member of the C. humilis complex.

Butcher includes a photograph of the plant in cultivation.  He notes that Knize uses the name C. tenuispina and wonders if this is a half way link between C. tocopillana and C. tenuissima.
[PK: ..... or perhaps a simple spelling mistake?]

Adriana Hoffmann still retains C. tenuissima as a good species.

Ritter 539: Copiapoa tenuissima F. Ritter (nom.. inval. Art. 37.1) - Taxon 12(1):31, 1963. (First mentioned in Backeberg, Die Cact. 6: 3840, 1962 (as nom. nud.). Based on 2 syntypes, Ritter 539 and Ritter 540 (U !). Erroneously included as valid in RPS 14.)
- Chile: mountains at the coast near Antofagasta. - One of the two syntype collection numbers of Copiapoa tenuissima.
ZSS S10450 - sem (Leg. Fa. Köhres (ex cult. ?) 1977.) 

Ritter 540: Copiapoa tenuissima F. Ritter (nom.. inval. Art. 37.1) - Taxon 12(1):31, 1963. (First mentioned in Backeberg, Die Cact. 6: 3840, 1962 (as nom. nud.). Based on 2 syntypes, Ritter 539 and Ritter 540 (U !). Erroneously included as valid in RPS 14.)

loc. 1:     Chile: mountains at the coast near Antofagasta. - One of the two syntype collection numbers of Copiapoa tenuissima.
SGO 125692 SYN - fl (,,Daten notiert“ = data recorded. ,,Die entzückende kleine dunkle (schwarze) Copiapoa 539+540 - Ich sehe keinen Unterschied. Es sind ausnahmsweise kleine Blüten (539 ist gleich) 540 Cop. tenuissima ( 541 ist Pilocopiapoa)“ = The enchanting small dark (black) Copiapoa 539+540 - I can‘t see any difference. These are exceptionally small flowers (539 is identical) 540 Copiapoa] tenuissima (541 is Pilocopiapoa). - it is not absolutely certain that this comment is by F. Ritter, it could also have been supplied by his sister H. Winter.)
SGO 125693 SYN - fl (,,Daten notiert“ = data recorded. The following comment is by F. Ritter‘s sister, H. Winter: ,,Siehst Du, solche Sachen, die hier beständig blühen, müsste man in Pflanzen haben.
[p311]
1) Sehr wichtig, dass Du sie schnellstens bestimmst, denn Backeberg hat sie bestimmt schon.

2) Ausnützen, so lange sie noch neu + gesucht ist, + Pflz. (ohne Rübe) nur Köpfe! zum Pfropfen hersenden + Samen.“ = You see, such things which constantly flower should be available as plants.

1) Very important that you identify them quickly, because Backeberg certainly has them already.

2) take advantage as long as they are new and in demand, and send plants (without taproot) only head ! for grafting, and seeds.)
U 1 17651B SYN - rad, corp, ar, sp (Labelled as ,,Holotypus“ by Ritter.)

loc. 2:     Chile: ,,El Cobre“. - One of the two syntype collection numbers of Copiapoa tenuissima.
SGO 124897 SYN - rad, corp. ar, sp
ZSS SR13487 SYN – sem

The authors focus on the environmental aspects, rather than the taxonomic issues.

Charles (1998) regards this taxon as a variety of Copiapoa humilis. 

Hunt D. (Ed.),  2002, Cactaceae Systematics Initiatives 13:12

Reduced to the rank of ssp:
Copiapoa hypogaea ssp tenuissima
As the original description is invalid, this is the actual basionym for the taxon.

As Copiapoa humilis subsp. tenuissima (Ritter ex Hunt) Hunt 2003