Thorneochloa diegoensis (Swallen) Romasch., comb. nov.,

Peterson, Paul M., Romaschenko, Konstantin, Soreng, Robert J. & Reyna, Jesus Valdes, 2019, 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, x Eriosella, Pseudoeriocoma, Ptilagrostiella, and Thorneochloa, PhytoKeys 126, pp. 89-125: 105-109

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Thorneochloa diegoensis (Swallen) Romasch., comb. nov.


Thorneochloa diegoensis (Swallen) Romasch., comb. nov. 

Stipa diegoensis  Swallen, J. Wash. Acad. Sci. 30(5): 212, f. 2. 1940 [Basionym] ≡ Achnatherum diegoense  (Swallen) Barkworth, Phytologia 74(1): 7. 1993. Type: USA, California, San Diego Co., Proctor Valley near Jamul, along vernal stream in chaparral, 23 May 1938, F. F. Gander 5778 (holotype: US-1761177!; isotypes: AHUC-30095 [image!], CAS-0005662 [image!], DAO-000465418 [image!], F-0044439F [image!], SD-00000072 [image!]). Fig. 5A-EView Figure 5.

Distribution and habitat.

Thorneochloa diegoensis  is found in Channel Islands (Santa Barbara County), San Diego, and Ventura Counties and Baja California, Mexico in rocky soil along vernal streams and canyons in chaparral and coastal sage-scrub vegetation; usually below 500 m ( Barkworth 2007; Calflora 2018).


Molecular sequence analysis reveals multiple origins of this taxon. In our preliminary ITS-derived phylogenetic tree Thorneochloa diegoensis  aligns within Nassella  whereas in the combined plastid-derived tree it aligns within Pseudoeriocoma  ( Valdés Reyna et al. 2013). Geographically, the most likely parents, if of hybrid origin, would be Nassella mucronata  (Kunth) R.W. Pohl and Pseudoeriocoma eminens  . A more detailed genetic study using low-copy nuclear genes would perhaps resolve this hypothesis.

A key to the native and introduced (marked with an asterisk) genera of Stipeae  (and Ampelodesmeae) in North America (modified from Barkworth 2007)

1 Spikelets with 2-6 florets; cultivated as ornamental, a Mediterranean species escaped in California Ampelodesmos  Link* (tribe Ampelodesmeae)
- Spikelets with 1 floret (tribe Stipeae  ); plants native or not 2
2 Paleas sulcate, longer than the lemmas; lemma margins involute, fitting into the paleal grove; lemma apices not lobed Piptochaetium 
- Paleas flat, from shorter than to longer than the lemmas; lemma margins convolute or not overlapping; lemma apices often lobed or bifid 3
3 Prophylls exceeding the leaf sheaths; lemmas with 2 prominent lobes at apex (0.9-2 mm long); plants cultivated as ornamentals, not escaped 4
- Prophylls concealed by the leaf sheaths; lemmas with mostly shorter lobed or unlobed apices; plants native, introduced from Mediterranean region, sometimes cultivated as ornamentals 5
4 Panicles contracted; lemma awns once-geniculate, first segment plumose; style 1 Macrochloa  *
- Panicles open; lemma awns twice-geniculate, segments glabrous; styles 2 Celtica  *
5 Plants with multiple stiff branches from the upper nodes; pedicels sometimes plumose; Australian species cultivated as ornamentals in the Flora region Austrostipa  *
- Plants not branching at the upper nodes, or with a few, flexible branches ( Pseudoeriocoma  ); pedicels never plumose; species native, established introductions, or cultivated as ornamentals 6
6 Apices of the leaf blade sharp and stiff; caryopses obovoid, often with 3 smooth ribs at maturity; cleistogenes usually present in sheaths; plants adventive in California, native from Mexico southward Amelichloa 
- Apices of the leaf blades acute to acuminate, never both sharp and stiff; caryopses fusiform, ovoid or obovoid, without ribs; cleistogenes sometimes present in sheaths 7
7 Lemma margins strongly overlapping over their whole length at maturity, lemma bodies usually rough throughout, apices with a membranous or indurate crown and not lobed; paleas ¼-½ the length of the lemmas, without veins, glabrous; plants native to North America and southward, South American species sometimes cultivated as ornamentals and escaped Nassella 
- Lemma margins usually not or only slightly overlapping for some or all of their length at maturity, strongly overlapping in some species with smooth lemmas, lemma bodies usually smooth on the lower portion, apices often 1-2-lobed and never with a membranous or indurate crown; paleas from 1/3 as long as to equaling or slightly exceeding the lemmas, 2-veined at least on the lower portion, usually with hairs or both lemmas and paleas glabrous 8
8 Calluses 1.5-6 mm long, sharply pointed; plants perennial or annual, if perennial, awns 65-500 mm long, if annual, awns 50-100 mm long; panicle branches straight 9
- Calluses 0.1-2 mm long, blunt to sharply pointed; plants perennial; awns 1-70 mm; panicle branches straight or flexuous 12
9 Lower ligules densely hairy, upper ligules less densely hairy or glabrous; awns plumose in lower segment, glabrous above, unigeniculate; plants perennial Pappostipa 
- Ligules glabrous or inconspicuously pubescent, lower and upper ligules alike in vestiture; awns glabrous or pilose throughout or in lower segment; plants perennial or annual 10
10 Plants perennial; florets 7-25 mm long; awns scabrous or pilose on the first 2 segments, the terminal segment scabrous, or if pilose, the hairs 1-3 mm long Hesperostipa 
- Plants annual or perennial, if perennial, the florets 18-27 mm long and the awns plumose on the terminal segment, the hairs 5-6 mm long 11
11 Plants annual; glumes 12-20 mm long; florets 4-7 mm long; awn sparsely short hairy in basal segment only; plants adventive from Mediterranean, noxious weeds in Southern California Stipelulla*
- Plants perennial (sometimes short-lived); glumes 60-90 cm long; florets 18-27 mm long; the awns plumose on the terminal segment, the hairs 5-6 mm long; plants cultivated ornamentals from Eurasia, not escaped Stipa  *
12 Panicles to 60 cm long, delicate, nodding, branches capillary, loosely spreading to spreading in distant whorls; lemmas 2 mm long, coarsely scabrous distally, mar gins meeting or slightly gapped; callus with a brief ring of hairs; awns caducous, to 8 mm long, slender, scabrous, curved; anther 1, 0.8-1.4 mm long, apically thickened, not penicilliate; plants cultivated ornamentals from New Zealand, not escaped Anemanthele  *
- Panicles of various lengths, and shapes (similar in Oloptum  , but lemma surfaces smooth, margins widely gapped in middle and fused at base, callus glabrous); lemmas usually longer; awns various; anthers 3, not apically thickened, penicillate or not; plants sometimes cultivated 13
13 Florets usually dorsally compressed at maturity, sometimes terete; paleas as long as or longer than the lemmas and similar in texture and pubescence; lemma margins separate for their whole length at maturity 14
- Florets terete or laterally compressed at maturity; paleas often shorter than the lemmas, sometimes less pubescent, sometimes as long as the lemmas and similar in texture and pubescence; lemma margins often overlapping for part or all of their length at maturity 17
14 Callus barbed with a dense ring of flexuous hairs, hairs 1.0-1.5 mm long; style 1; lodicules 2; elongated leaf blades concentrated basally (above initial cataphylls), upper cauline leaves much reduced, only 0.8-1.8 cm long; lemma epidermal pattern saw-like Oryzopsis 
- Callus glabrous or with short straight hairs forming a sparse ring, hairs 0.1-0.5 mm long; styles 2; lodicules 2 or 3; awn central; cauline leaves well developed, similar to basal leaves, or somewhat shorter but not strongly reduced; lemma epidermal pattern saw-like or maize-like 15
15 Glumes 5-9-veined, with faint or prominent transverse veinlets; basal leaf blades absent (leaves cataphyllous) then up to 2 cm long; mid- and upper cauline leaves several, up to 35 cm long and 2 cm wide Patis 
- Glumes 1-3-veined, transverse veinlets absent (rarely present, never prominent); basal leaf blades well developed or not (leaves cataphyllous or not), mostly 2-90 cm long or reduced; cauline leaves similar to basal leaves, or sometimes shorter or rudimentary 16
16 Plants with well-developed basal tufts leaves, blades slender; central vein of the lemma not prominent; lower panicle branches never whorled; anther apices glabrous; lemma epidermal pattern Saw-like; awns caducous and straight and basally slightly twisted, or persistent and geniculate with a strongly twisted first segment; plants native Piptatheropsis 
- Plants without basal tufts of leaves, blades 2-10 mm wide; central vein of the lemma prominent; lower panicle branches whorled with 3-30 or more per node; anther apices minutely bearded; lemma epidermal pattern Maize-like; awns persistent or caducous, straight, never twisted; plants adventive from Eurasia Oloptum  *
17 Glumes without evident venation, glume apices rounded to acute; plants subalpine to alpine, sometimes growing in bogs 18
- Glumes with 1-3(5) evident veins or the glume apices attenuate; plants growing from near sea level to subalpine or alpine habitats, not growing in bogs 19
18 Awns strigillose in lower part; lemma lobes inconspicuous (0.1-0.4 mm); callus sharp; panicles narrow to loosely contracted; anthers penicillate, 0.5-1.5 mm long Ptilagrostiella 
- Awns hairy throughout, lemma lobes prominent (up to 0.8 mm); callus blunt; the hairs on the lowest segment 1-2 mm long; panicles open with spreading branches these sometimes loosely contracted; anthers glabrous, 1.2-3 mm long Ptilagrostis 
19 Paleas with prolonged veins almost reaching the tip of the lemma lobes, the veins 1-3 mm long; lemma apices 2-lobed, narrow, the lobes 1-3 mm long Barkworthia 
- Paleas without prolonged veins or if prolonged never more than 0.3 mm long; lemma apices unlobed or if lobed, the lobes usually obtuse and never more than 2.1 mm long 20
20 Lemma bodies with hairs to 0.15 mm long over most of their length, and a tuft of pappus-like hairs at the apex to 3-4 mm long; awns glabrous; ligules with lateral tufts of hairs to 2 mm long; anthers 0.8 mm long; plants native from Mexico southward, infrequently cultivated as an ornamental Jarava 
- Lemma bodies with evenly distributed hairs of similar length or completely glabrous, sometimes with longer hairs around the base of the awn; basal segment of the awns sometimes with hairs up to 2 mm long; ligules without lateral tufts of hairs; anthers mostly longer; plants of Mexico and northward, infrequently cultivated as an ornamentals 21
21 Basal leaf sheaths becoming fibrous with age; panicle branches whorled below; apical lemma hairs 1-1.5 mm long; awns readily deciduous; upper culm ligules to 12 mm long; plants cultivated ornamentals from Asia, uncommon, not known to have escaped Neotrinia  *
- Basal leaf sheaths never fibrous, occasionally ribbon-like; panicle branches rarely whorled below; lemmas usually without apical lemmas hairs longer than those present on the body; upper culm ligules usually less than 5 mm long; plants native and widespread 22
22 Plants with woody, sometimes scandent bamboo-like culms, 3-6 mm thick below with ramified branching (usually, but sometimes absent in immature specimens of P. hirticulmis  ) at the middle and upper nodes, with (2) 3 to 13 nodes Pseudoeriocoma 
- Plants with neither woody nor scandent bamboo-like culms, usually less than 2 mm thick below and never with ramified branching at the middle and upper nodes, with 2 to 3 or up to 5 nodes in a few species 23
23 Lower culm internodes densely pubescent for 3-9 mm below the nodes, the hairs retrorse with shorter hairs and less densely pubescent elsewhere; known only from southern California and Baja California Thorneochloa 
- Lower culm internodes glabrous or if pubescent then only to 5 mm below the nodes, usually glabrous elsewhere or if hairy the hairs usually not retrorse; widely distributed in western North America Eriocoma 

Excluded name














Thorneochloa diegoensis (Swallen) Romasch., comb. nov.

Peterson, Paul M., Romaschenko, Konstantin, Soreng, Robert J. & Reyna, Jesus Valdes 2019

Achnatherum diegoense

Barkworth 1993

Stipa diegoensis

Swallen 1940