Thorneochloa

{{see also|Glossary of leaf morphology|Glossary of plant morphology|Glossary of botanical terms}}

Thorneochloa diegoensis is a bunching perennial grass with culms (stems) between {{cvt|70|-|140|cm|in}} tall in an erect or ascending habit. The culms are {{cvt|2|-|4|mm|in}} thick, and characteristically {{cvt|3|-|9|mm|in}} below the lower nodes the internodes have a dense pubescence of retrorse (pointing downward) hairs. The leaf sheath may be glabrous or pubescent, and the collar with a tuft of hairs that measure {{cvt|1.5|-|2|mm|in}} long. The leaf blades are {{cvt|15|-|40|cm|in}} long by {{cvt|1|-|3.5|mm|in}} wide.{{Cite journal |last1=Peterson |first1=Paul M. |last2=Romaschenko |first2=Konstantin |last3=Soreng |first3=Robert J. |last4=Valdés Reyna |first4=Jesus |date=2019-07-16 |title=A key to the North American genera of Stipeae (Poaceae, Pooideae) with descriptions and taxonomic names for species of Eriocoma, Neotrinia, Oloptum, and five new genera: Barkworthia, ×Eriosella, Pseudoeriocoma, Ptilagrostiella, and Thorneochloa |journal=PhytoKeys |issue=126 |pages=89–125 |doi=10.3897/phytokeys.126.34096 |doi-access=free |issn=1314-2003 |pmc=6650443 |pmid=31360096|bibcode=2019PhytK.126...89P }}

The inflorescence, a narrow, densely-flowered panicle, is up to {{cvt|30|cm|in}} long, with ascending, appressed branches. The pedicels are usually shorter than the spikelets. The spikelet is lanceolate with a single fertile floret. The glumes are {{cvt|8|-|11.5|mm|in}} long. The floret and lemma are {{cvt|5.5|-|7.5|mm|in}} long, the lemma evenly hairy and its margins enveloping most of the palea. The lemma is 1.3 to 2 × longer than the palea, and has a long scabrous awn {{cvt|20|-|50|mm|in}} long that is bent twice. Flowering is typically from March to June.

Thorneochloa diegoensis was first described as Stipa diegoensis by Jason Richard Swallen in 1940 based on specimens collected by Frank F. Gander in Proctor Valley.{{cite journal |last1=Swallen |first1=Jason R. |title=Miscellaneous new American grasses |journal=Journal of the Washington Academy of Sciences |date=1940 |volume=30 |page=212 |url=https://www.biodiversitylibrary.org/page/39700244#page/242 |access-date=5 June 2025 |publisher=Washington Academy of Sciences |location=Washington, D.C.}} It was later transferred into the genus Achnatherum by Mary Barkworth in 1993, along with many grasses mostly segregated from Stipa as part of a new delineation of the North American Stipeae.{{cite journal |last1=Barkworth |first1=Mary E. |title=North American Stipeae (Gramineae): Taxonomic changes and other comments |journal=Phytologia |date=January 1993 |volume=74 |issue=1 |pages=1-25 |url=https://www.biodiversitylibrary.org/page/13068903#page/3 |access-date=5 June 2025}}

A reorganization of the Stipeae tribe based on molecular phylogenetics by Peterson et al. in 2019 resulted in the new monotypic genus Thorneochloa and a new combination for this species, Thorneochloa diegoensis. Thorneochloa is part of a strongly-supported clade with Achnatherum that is characterized by a maize-like epidermal pattern on the lemma. The genus is named in honor of botanist Robert Folger Thorne.

Thorneochloa diegoensis is native to southern California and northern Baja California. It occurs on all of the northern Channel Islands and San Nicolas Island, and on the mainland in San Diego County in the Peninsular Ranges, continuing south across the international border along the coast of Baja California to San Quintín and Isla Todos Santos.{{Cite journal |last1=Rebman |first1=Jon P. |last2=Gibson |first2=Judy |last3=Rich |first3=Karen |date=15 November 2016 |title=Annotated Checklist of the Vascular Plants of Baja California, Mexico |url=http://sdplantatlas.org/pdffiles/BajaChecklist2016.pdf |journal=Proceedings of the San Diego Society of Natural History |publisher=San Diego Natural History Museum |volume=45 |pages=289 |via=San Diego Plant Atlas}} It is a resident of chaparral and coastal sage scrub ecosystems below 350 feet in elevation, especially near streams.[https://web.archive.org/web/20110611141946/http://herbarium.usu.edu/webmanual/info2.asp?name=Achnatherum_diegoense&type=treatment Grass Manual Treatment]

{{Reflist}}

• [https://ucjeps.berkeley.edu/eflora/eflora_display.php?tid=45664 Jepson Manual Treatment]
• [https://plants.usda.gov/java/profile?symbol=ACDI10 USDA Plants Profile]
• [https://web.archive.org/web/20110611141946/http://herbarium.usu.edu/webmanual/info2.asp?name=Achnatherum_diegoense&type=treatment Grass Manual Treatment]
• [http://calphotos.berkeley.edu/cgi/img_query?query_src=photos_index&where-taxon=Achnatherum+diegoense Photo gallery]

{{Taxonbar|from1=Q94089709|from2=Q94304387|from3=Q4673849|from4=Q15505046}}

Category:Stipeae

Category:Monotypic Poaceae genera

Category:Bunchgrasses of North America

Category:Grasses of Mexico

Category:Native grasses of California

Category:Flora of Baja California

Category:Natural history of the California chaparral and woodlands

Category:Natural history of the Channel Islands of California

Category:Natural history of the Peninsular Ranges

Category:Grasses of North America

Category:Plants described in 1940