Flora of North America species comparison

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Ceanothus papillosus

Ceanothus arcuatus

wartleaf ceanothus

arching ceanothus
Habit Shrubs, evergreen, 1–5 m. Stems erect to ascending, not rooting at nodes; branchlets green to reddish brown, not thorn-tipped, round in cross section, ± flexible to rigid, densely tomentulose. Shrubs, 0.3–0.8 m, moundlike.
Stems

ascending or spreading, not rooting at nodes;

branchlets brown to grayish brown, ± rigid, tomentulose, glabrescent.
Leaves

petiole 1–3 mm;

blade cupped to flat, linear, narrowly oblong, or oblong-elliptic, 12–50 × 6–15 mm, base obtuse to rounded, margins minutely glandular-denticulate, revolute, glands 17–31, apex obtuse, truncate, or retuse, abaxial surface pale green, densely villosulous to tomentulose, adaxial surface dark green, sparsely puberulent and glandular-papillate; pinnately veined.

sometimes fascicled, axillary short shoots ascending to spreading;

petiole 1–2 mm;

blade flat, elliptic to oblanceolate, 4–10 × 2–5 mm, base rounded, margins thick, not revolute, usually entire, rarely denticulate near apex, teeth 1–3, apex rounded to obtuse, abaxial surface green to pale green, glabrate, adaxial surface pale green, glabrous.
Inflorescences

axillary or terminal, racemelike, 2–8 cm.

axillary or terminal, 0.8–2.5 cm.
Flowers

sepals, petals, and nectary deep blue.

sepals and petals white to pale blue;

nectary pale blue or yellow tinged.
Capsules

2–3 mm wide, lobed;

valves smooth, viscid when young, not or weakly crested.

4–6 mm wide, not to weakly lobed;

valves smooth to rugulose, horns subapical, prominent, erect, intermediate ridges absent.
2n

= 24.

Ceanothus papillosus

Ceanothus arcuatus
Phenology Flowering Mar–May. Flowering May–Jun.
Habitat Rocky ridges, slopes, and flats, chaparral, mixed evergreen forests. Granitic or serpentine soils, conifer forests.
Elevation 20–1500 m. (100–4900 ft.) 900–2300 m. (3000–7500 ft.)
Distribution
from FNA
CA; Mexico (Baja California)
[WildflowerSearch map]
[BONAP county map]
from FNA
CA; OR
[BONAP county map]
Discussion

Ceanothus papillosus occurs in the Coast Ranges from San Francisco Bay south to the Santa Ynez Mountains, Ventura County, with disjunct populations in the Santa Ana Mountains, California, and Cerro Bola, in northern Baja California. The name C. papillosus var. roweanus was originally applied to low-growing plants with ascending to spreading, arcuate branches (H. McMinn 1939). M. Van Rensselaer and McMinn (1942) later emended the circumscription to include plants with linear leaves and retuse to truncate leaf apices, but these are found throughout the range of the species. Leaves with obtuse to truncate or retuse leaf apices also can be found on the same plant. Putative hybrids with C. integerrimus and C. oliganthus have been documented (McMinn 1944). Hybrids with C. thyrsiflorus have been named C. ×regius (Jepson) McMinn. Some putatively advanced generation hybrids have narrowly elliptic, weakly papillate leaves with obtuse apices, and sometimes have been misinterpreted as belonging to C. papillosus.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Ceanothus arcuatus was explicitly described as a species by McMinn but inexplicably treated as a hybrid between C. fresnensis and C. cuneatus by P. A. Munz (1959). Munz may have been influenced by McMinn’s hypothesis that C. arcuatus was derived through hybridization between the two species. Some specimens from the Klamath Mountains have been either interpreted as C. cuneatus or misidentified as hybrids between C. pumilus and C. cuneatus. Populations of C. arcuatus are relatively uniform throughout their geographic distribution and often represent the dominant understory shrub in conifer forests of the Klamath Mountains and Sierra Nevada. Ceanothus arcuatus occurs primarily on metamorphic substrates in the Klamath Mountains and the northern Sierra Nevada, but in the central Sierra Nevada (Nevada County south to Madera County), the most common substrate is granitic.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 12, p. 92. FNA vol. 12, p. 101.
Parent taxa Rhamnaceae > Ceanothus > subg. Ceanothus Rhamnaceae > Ceanothus > subg. Cerastes
Sibling taxa
C. americanus, C. arboreus, C. arcuatus, C. confusus, C. cordulatus, C. crassifolius, C. cuneatus, C. cyaneus, C. dentatus, C. divergens, C. diversifolius, C. fendleri, C. ferrisiae, C. foliosus, C. fresnensis, C. gloriosus, C. griseus, C. hearstiorum, C. herbaceus, C. impressus, C. incanus, C. integerrimus, C. jepsonii, C. lemmonii, C. leucodermis, C. maritimus, C. martini, C. masonii, C. megacarpus, C. microphyllus, C. oliganthus, C. ophiochilus, C. otayensis, C. palmeri, C. parryi, C. parvifolius, C. pauciflorus, C. perplexans, C. pinetorum, C. prostratus, C. pumilus, C. purpureus, C. roderickii, C. sanguineus, C. sonomensis, C. spinosus, C. thyrsiflorus, C. tomentosus, C. velutinus, C. verrucosus
C. americanus, C. arboreus, C. confusus, C. cordulatus, C. crassifolius, C. cuneatus, C. cyaneus, C. dentatus, C. divergens, C. diversifolius, C. fendleri, C. ferrisiae, C. foliosus, C. fresnensis, C. gloriosus, C. griseus, C. hearstiorum, C. herbaceus, C. impressus, C. incanus, C. integerrimus, C. jepsonii, C. lemmonii, C. leucodermis, C. maritimus, C. martini, C. masonii, C. megacarpus, C. microphyllus, C. oliganthus, C. ophiochilus, C. otayensis, C. palmeri, C. papillosus, C. parryi, C. parvifolius, C. pauciflorus, C. perplexans, C. pinetorum, C. prostratus, C. pumilus, C. purpureus, C. roderickii, C. sanguineus, C. sonomensis, C. spinosus, C. thyrsiflorus, C. tomentosus, C. velutinus, C. verrucosus
Synonyms C. papillosus subsp. roweanus, C. papillosus var. roweanus
Name authority Torrey & A. Gray: Fl. N. Amer. 1: 268. (1838) McMinn: in M. van Rensselaer and H. McMinn, Ceanothus, 247, fig. 82. (1942)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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