Campanula exigua

Rattan, Bot. Gaz. (Crawfordsville) 11:339. 1886. non Formanek, 1894. - Type: California, Contra Costa Co., summit of Mt. Diablo, 14 June 1886, V. Rattan s.n. (Holotype:JEPS!; Isotypes: GH! JEPS!). The Rattan collection at GH contains a holograph description of the new species with a postcard sent to Coulter that mentions Mrs. Curran's Mt. Tamalpais collection. There is no indication on that specimen that it is the holotype. The sheets at JEPS were deposited there after Rattan's death by his daughter, according to Jepson's notes, and had been part of Rattan's personal herbarium. In the pocket of one, marked “type” in Jepson's hand, is a loose label with imprinted locality information and “Campanula githopsidea” handwritten. On the reverse of the label is a note in Rattan's handwriting to the effect that Gray had suggested Campanula exgua instead bevause he considered the former name confusing. It seems reasonable to treat this JEPS sheet as the holotype.1)

It is suggested that Campanula griffinii is closely related to Campanula exigua.2)
All of the California annuals (Campanula angustiflora, Campanula exigua, Campanula sharsmithiae and Campanula griffinii) have been a source of confusion since their discovery, judging from the misidentifications found in herbaria, and they are not known to be closely related to any other campanulas. Treatment of small-flowered and annual Old World campanulas has been controversial (Boissier, 1874; de Candolle, 1830; Gadella, 1964, 1966; Federov, 1957), and knowledge of New World campanulas is very limited (Shetler, 1963). Here I give detailed descriptions of the Californian annual campanulas in order to facilitate eventual comparison between them and their Nort American relatives and between them and their Mediterranean counterparts.3)

Taxonomic History

W.H. Brewer (1867) made the earliest known collection of this group in 1862 on Mt. Hamilton (Santa Clara Co.) just a few days after he had found its striking associate, Clarkia breweri (A. Gray) Greene. Gray never assigned a species name to the specimen, and this campanula was not collected again until Rattan found it on Mt. Diablo (Contra Costa Co.) and described it as Campanula exigua (Rattan, 1886). In his description, Rattan referred to a plant taken that same year by Mrs. Curran on Mt. Tamalpais (Marin Co.). Alice Eastwood (1898) included the Mt. Tamalpais plant in Campanula angustiflora Eastwood. In her discussion of the new species, Eastwood referred to “very young specimens of an annual Campanula” collected in Priest Valley (Monterey Co.) that shared some characteristics with both named taxa, but that she chose to retain in Campanula angustiflora. Howell (1938) eventually described this plant as Campanula angustiflora var. exilis, herein named Campanula griffinii.4)



Erect annuals, 5-25cm high; stems 4-angled, glabrous or hispid below the first flowers, or all parts hispid.

Both Campanula exigua and Campanula griffinii have narrow, somewhat sclerophyllous leaves and bracts. The bracts in both species are arranged near the apex of each branch but at least 4mm and more often 7-8mm apart. Consequently, subsequent branches are arranged alternately. Because the flowers of Campanula exigua have long pedicels and the branches are widely spaced, the plants appear very open and delicate. In contrast, the bracts of Campanula sharsmithiae are opposite or nearly so and the branches, both of which usually develop, seem superficially to be truly dichotomous. The fleshy leaves are wider than those of Campanula exigua and the plants of Campanula sharsmithiae accordingly appear to be leafier and generally denser.5)


Morphological simularities of these taxa to other Nort American Campanulideae may be due to convergence; consequently, the relationships of these four species (Campanula angustifloar, Campanula exigua, Campanula sharsmithiae and Campanula griffinii) are obscure.

The flower structure of Campanula exigua is typical of campanulas and in terms of flower morphology Campanula exigua and Campanula sharsmithae retain the most primitive characteristics of the annual species discussed here.

Rattan (1886) pointed out the morphological resemblance of Campanula exigua to Githopsis, another annual member of western North American Campanuloideae. Githopsis pulchella Vatke, the only obligately outcrossed species in that genus, and Campanula exigua are vegetatively almost identical and have very similar flowers. They differ in capsule structure, which is long, narrow, deeply ridged, and apically dehiscent in Githopsis. Githopsis pulchella has n = 10, 6-porate pollen, and striate, fusiform seeds. These differences suggest that these two species are similar because of convergence rather than direct relationship.6)

Campanula exigua is also vegetatively similar to Campanula reverchonii an annual that is endemic to granitic outcrops in central Texas (Shetler, 1963); however, its capsule and seed morphology differ strikingly from those of Campanula reverchonii. Again, convergence rather than close relationship is suggested.
The combination of character states shared by Campanula griffinii and Campanula exigua seems to support the hypothesis that Campanula griffinii arose from a Campanula exigua-like ancestor. These character states are: narrow leaves, upper bracts closer to the flower than to the subtending leaf, longest leaf subtending first flower, capsules cylindrical with inter-rib area not infolded or tuberculate, seeds not fusiform, flattened at chalazal end, pollen pantoporate, n = 17. Because Campanula griffinii differs quantitatively in most characters from Campanula exigua, has a different breeding system, and has an independent geographical range, I consider them distinct.7)


Narrow leaves, opposite bracts less wider than those of Campanula sharsmihiae.

Lower cauline leaves sessile, alternate, 4-7mm long, broadly spatulate, obtuse, few-toothed, abaxial side glabrous or hispid; upper cauline leaves (5-)7-11mm long, linear-subulate, 6-14 times as long as broad, acute, with 4 pairs of narrow, shallow, gland-tipped teeth, abaxial side glabrous or hispid; longest leaf subtends first flower; bract sessile, 4-7.5mm long, linear-subulate, 6.5-15 times as long as broad, acute, few-toothed, lower bract closer to flower than the leaf subtending branch but the two bracts of each branch (4-)7-10(-21)mm apart.


May-Jun; Large flowers, pedicel (2-)7-15mm long, usually curved,; corollas 7.4-11(-18)mm long, 3-4.5 times as long as ovary, funnelform-campanulate, pale blue to white with fine, blue, longitudinal lines, throat more UV absorbing than lobes; lobes 5, about half the length of the corolla, twice as long as broad, acute, reflexed; corolla papillate internally at base and along sides beneath sinuses; style blue, 6-8mm long, papillate distaly two-thirds its length; style lobes 08-1.2mm long, tightly appressed at anthesis; stamens 4.3-5.5mm long, anthers twice the length of filaments, filaments abruptly dilated to a wide, ciliate base; pollen 12-pantoporate, 0.035mm dia.; ovary 1.7-2.9mm long, about as long as broad, conical at base, the sides cylindrical, strongly ribbed, the inter-rib area not infolded or tuberculate, 2-3 times as long as ovary, twice to nearly equal capsule, erect in fruit. 8)


Pantopotate pollen.

Most European Campanula pollen studied to date is 3- to 4-porate (Dunbar, 1975). Most North American campanulas (and other North American genera in Campanuloideae) have pollen that is 5- to 6-porate, the pores equatorial )Chapman, 1966; Chuang, pers. comm., 1978; Morin, unpubl. data). Only Campanula americana L., Campanula exgua, and Campanula griffinii are known to have pantoporate pollen, although pores of Campanula reverchonii are not strictly equatorial. Small (1903) placed Campanula americana in the monotypic genus Campanulastrum, and Gadella (1964) supported this decision. There is little morphological similarity between Campanula americana (which is a tall, broadleaved annual or biennial with spicate inflorescences and rotate corollas) and the annual California campanulas. Therefore it seems likely that pantoporate pollen evolved independently in these two groups.9)


n = 17 10)


Capsule 2.8-5.4mm long, about as long as broad, strongly ribbed; pore midway between base and apex; ovules 60-100, seeds 0.65-0.73mm long, oblong, elliptical in cross-section, about twice as long as wide, flat on chalazal end, light brown, shiny, finely striate (Fig.1).11)


Four of the ten species of Campanula that are found in the California Floristic Province are annuals; Campanula exigua - Grows in the inner South Coast Ranges from Mt. Diablo to southern San Benito Co. (Fig.4). 12)

Fig.4. Distribution of annual California campanulas.


Scattered individuals on talus slopes, 300-1250m.

The slopes on which Campanula sharsmithiae is found are nearly devoid of soil or grass cover and are very unstable. Campanula exigua grows on more gradual slopes that have a sparse covering of grass and other small herbs.


Seeds of field-collected plants were grown at the University of California Botanical Garden in pots of “UC Mix, formula C” soil (Matkin and Chandler, 1957), in insect exclosures, for studies of morphology, cytology, and pollination system. Seed sources are indicated in the Taxonomic Treatment and included at least one northers and one southern population of each species except Campanula sharsmithiae, seeds of which were not available. Voucher specimens are in UC.

Buds from field-collected and garden-grown plants were preserved in Carnoy's 6:3:1 solution; microsporocytes were stained in acetocarmine for chromosome preparations. Pollen was mounted in lactophenol and cotton blue for study of general morphology and was prepared following the method of Lynch and Webster (1975) for study of exine ultrastructure, except that material was CO2-critical-point-dried directly from 100 percent ethanol. After initial preparation the pollen was coated with 30nm of gold palladium and viewed on a Coates and Welter Model 50 Emission Scanning Electron Microscope.

Measurements of vegetative and floral parts were made on pressed, garden-grown plants and on herbarium specimens from BR, CAS, CU, DAV, DS, GH, JEPS, K, MICH, MO, ND, NO, NY, ORE, OSC, PH, POM, RSA, SBBG, UC, UCSB, US, UTC, WS, and WTU. Corollas of living plants were photographed in direct sunlight with a Tiffin 18A Photar filter with high speed Ektachrome and Tri-X films to document ultraviolet (UV) absorptions patterns.

Flowers of carpellate parents in artificial crosses were emasculated before anthesis and later pollinated by transferring pollen from the style of the staminate parent, on sterile forceps, to the stigmatic surface of the carpellate parent. Except when they were being manipulated, the flowers were covered with Kimwipe bags before anthesis with no further treatment. Self-compatibility of Campanula exigua was tested by transferring pollen from the style to the stigma of the same flower. Pollen is deposited on the stigmatic area of Campanula angustiflora and Campanula griffinii before anthesis and therefore was not artificially transferred. Presence of apomixis was tested by leaving emasculated flowers unpollinated.

Results of methods

The two most obvious characters that separate these annual species are leaf width and corolla size (Figs. 1 and 2).

Fig.1. A. Campanula exigua Rattan (after Griffin 4141, UC). B. Campanula griffinii Morin (after Griffin 4120, UC). C. Campanula angustiflora Eastwood (after Morin 249, UC). Habits: scale bar=1 cm. Details )sty=style, sta=stamen, co=corolla, f=flower):scale bar=1 mm.
Fig.2. Campanula sharsmithiae Morin (After Morin 299, UC). Habit: scale bar=1 cm. Details (sty=style, sta=stamen, f=flower): scale bar=1 mm; (h=hair): scale bar=o.1 mm.

Campanula exigua and Campanula sharsmithiae have large flowers. The former has thin, narrow leaves and the latter has fleshy, broader leaves. Campanula griffinii has narrow leaves and small flowers, and Campanula angustiflora has broad leaves and small flowers. These species also differ in ovary shape, filaments shape, and position of upper bracts. These characters, along with flower size and leaf shape, are more constant under garden conditions than most other characters. For this reason, they were chosen as major, differentiating characters.

Campanula exigua, Campanula sharsmithiae and Campanula griffinii have n = 17, wheras Campanula angustiflora has n = 15; they are the first annual campanulas reported to have these numbers. At least two populations of each species (only one for Campanula sharsmithiae) were counted; vouchers are deposited in UC and indicated in the Taxonomic Treatment.

Campanula exigua has 12-pantoporate pollen, Campanula sharsmithiae has 14-20 pantoporate pollen, and Campanula griffinii has 8-pantoporate pollen (Fig.3). Pantoporate pollen in Campanulaceae has previously been known only from Campanula americana (Dunbar, 1975), Campanula angustiflora has 6-porate pollen, the pores equatorial (Fig.3). Following the terminology used by Dunbar (1975), pollen sexine fine structure for the species studied can be described as short ridges, tip end bent upwards, with basally divided spinules (Fig.3).

Fig.3. a, b. Campanula angustiflora. c, d. Campanula griffinii. e, f. Campanula exigua. a, c, e. Pollen grains, scale bars=5mu m. b, d, f. Detail of exine, scale bars=0.5 mu m.

Reciprocal crosses among all species were unsuccessful. Unemasculated, bagged flowers and unbagged flowers of Campanula angustiflora and Campanula griffinii set seed (50-80 seeds per capsule), but emasculated, unpollinated flowers did not produce seed. These two species are self-pollinating and self-compatible; they do not appear to be apomictic, but pseudogamy cannot be ruled out. No flowers of Campanula exigua produced seed. Since even control, intrapopulational crosses were unsuccessful even though flowers in the field produce up to 100 seeds each, failure may have been due to technical problems such as mechanical damage to the stigma. Campanula exigua is not self-pollinating and seems to be self self-incompatible.

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campanula/exigua.txt · Laatst gewijzigd: 2012/11/05 18:53 door