Salicicola Translations

Examples of close Euro-American connections:

Two Mediterranean species of Salix

A. K. Skvortsov

Euro-amerikanische verwandtschaftliche Beziehungen zweier mediterraner Salix-Arten
Feddes Repertorium 1971, 82 (6): 407-420. Berlin

Translated from German by Irina Kadis

Translator's Note: This article was written 36 years ago. We are providing the entire text, the way it was published in German, except for the lists of herbarium specimens. According to the author himself, this treatment is now partially outdated--particularly as regards the Californian willows. However, the author has not changed his opinion regarding S. tristis and S. humilis.
According to the contemporary treatment by G. Argus (1997), the American species mentioned in this article are placed as follows: S. lasiolepis and S. irrorata to sect. Mexicanae; S. lemmonii and S. geyeriana to sect. Geyerianae. As for S. hookeriana, G. Argus has placed it together with S. humilis var. humilis and S. humilis var. tristis in sect. Cinerella, which corresponds to sect. Vetrix subsect. Laeves in Skvortsov (1968). This section as well includes the European species: S. aurita, S. caprea, S cinerea.
The translator is grateful to Anett Hofmann (University of Zurich) for advice on some difficulties with German.
The author shows a close relationship between Salix salviifolia Brotero, a species distributed across the Iberian Peninsula, and the eastern North American S. tristis Ait. Both species, along with the European S. aurita L. and American S. humilis Marsh., form a group of closely related species within the subsect. Laeves, sect. Vetrix.
Salix pedicellata Desf., a species with broad Mediterranean distribution, is related to the western North American (mostly Californian) S. lasiolepis Benth. The latter relationship, though it appears to be more distanced than the former, is also apparent. S. lasiolepis along with the closely related S. hookeriana Barr. present a western North American counterpart of the Old-World group of S. pedicellata within the subsect. Vulpinae. The available botanical evidence supports the hypothesis of direct trans-Atlantic origin of these connections rather than the explanation employing complicated migratory processes across Beringia and East Asia.
The phylogenetic relationships between willows of the Old and New World so far rarely have been a subject of discussion. The only study was undertaken in the 19th century by the renowned Salix researcher N. J. Andersson (1858, 1868). Andersson's conclusion was that "of 58 North American species, 24 are identical with European ones; 24 belong to the same types, and only 10, either western or Arctic forms, seem to be peculiar to this great continent." (Andersson 1858). Though this researcher succeeded in pointing out a number of valid connections, this conclusion of his today presents only historic interest. The number of willow species known from North America has grown more than twofold. Besides, the number of species common with Europe is only half as large. If we take into account the five European species that are widely cultivated in North America and naturalized, then the total number of common species is still only 12. From the perspective of contemporary knowledge, the majority of Andersson's conclusions as regards species relationships appear incorrect. (For example, he related S. coulteri and S. lasiolepis to the European S. daphnoides; S. barklayi to S. glauca; S. phlebophylla to S. retusa; he also considered S. lucida to be a subspecies of S. pentandra, etc.)
The relationships of the Old- and New-World willows have never been revised since Andersson's time. Taxonomic research on the American and European willows went on along two completely separate paths, totally independently. C. K. Schneider (1920a, b) was studying Eurasian willows, while his monographic description of the American species was not completed. Most importantly, Schneider followed the American tradition in his revision of the American willows and never succeeded to compare the sections delimited within the New World with those described in the Old World.
At present we have sufficient information only on the latest (apparently Quaternary) Eurasiatic-American relationships within the genus Salix. They are manifested first and foremost among Arctic, Arctic-Alpine, and sub-Arctic species that are common for both hemispheres (Salix reticulata L., S. vestita Pursh, S. herbacea L., S. polaris Wahlenb., S. phlebophylla Anderss., S. rotundifolia Trautv., S. glauca L., S. ovalifolia Trautv., S. arctica Pall., S. chamissonis Anderss., S. fuscescens Anderss., S. lanata L., S. alaxensis Coville, S. pulchra Cham., S. sphenophylla A. Skv.[1] Specimens of the latter species from Alaska were identified by Hulten (1968) as S. arctica ssp. torulosa . ) and also in the boreal S. bebbiana Sarg. Close affinity of the boreal American species S. serissima Fern., S. planifolia Pursh, and S. pedicellaris Pursh with the Eurasian S. pentandra L., S. phylicifolia L., and S. myrtilloides L. has been long known. The author has highlighted (Skvortsov 1966) close connections between the Siberian S. boganidensis Trautv. and S. erythrocarpa Kom. on one side and the American S. arbusculoides Anderss. and S. nivalis Hook. on the other side. Hulten (1968) has noticed the presence of S. hastata, an Old-World species, in Alaska. These examples repeatedly refer to just Arctic and Arctic-Alpine species. For the majority of American willows, the Old-World relations remain unknown. Clarification of these connections presents the most important and challenging goal of the Salix research.
This work is an attempt to approach the task through clarifying relationships of two European willows, Salix pedicellata Desf. and S. salviifolia Brot., with American species. These links might present interest not just for the willow research, but also to some extent for the study of the Mediterranean flora and its connections.
Studied material and acknowledgements
This work is largely based on the study at the Herbarium of the Botanic Institute in Leningrad (Curator Prof. I.T.Vassilczenko). Prof. G.Moggi has kindly made it possible for me to handle extensive material from the Herbarium of Florence University. Rich and valuable collections of S. salviifolia were received as exchange from Dr. A.R.Pinto da Silva (Oeiras, Portugal). Some American samples were provided by Prof. C.L.Hitchcook, Dr. Th.Crovello, and Dr. P.H.Raven from the United States. A number of samples were studied by the author in the Botanical Museum in Copenhagen (Director Dr. A.Skovsted). Many thanks to all the colleagues.
Relations of Salix salviifolia Brot.
The geographic area of this species is entirely within the Mediterranean Floristic Area, provided that the Area is delimited in the modern sense (see Meusel, Jäger, Weinert 1965). Yet S. salviifolia is not purely Mediterranean or sub-Mediterranean; even more appropriately it might be called Mediterranean-Atlantic. This is true not only because it is distributed on the Atlantic Coast, but also since it is more abundant in the western areas of the Iberian Peninsula, in Portugal, than in the inner parts or Mediterranean-Sea-facing areas of the peninsula. S. salviifolia has not been found anywhere outside the Iberian Peninsula.
The dense white-wooly tomentum of the lower leaf side is characteristic for S. salviifolia. Indeed the species received its name because of this tomentum. This kind of tomentum is found in species of sect. Villosae (S. lapponum L., S. alaxensis Coville, S. helvetica Vill., S. kryloviiE. Wolf, S. candida Willd.) as well as in sect. Canae (S. elaeagnos Scop.) Due to this similarity, some authors (Andersson 1868, Pereira Coutinho 1899) were inclined to place S. salviifolia close to the named sections. Yet in the rest of its characters S. salviifolia is rather different from the species of these sections. It should without doubt be assigned to sect. Vetrix (Vicioso 1951, Skvortsov 1968). More than that, sections Canae and Villosae belong to a phylogenetic line that is entirely different from that of sect. Vetrix. The white villous trichomes of S. salviifolia constitute one of many examples of parallelism and convergence, which is so widespread in the genus Salix (Skvortsov 1968). In other species of sect. Vetrix (such as, for example, S. pedicellata Desf. or S. kuznetzowii Goerz), one can also find specimens with nearly just as white and dense hairs.
Among Eurasian willow species, it is S. aurita L. that is the closest to S. salviifolia. From the first glance the two species look rather unlike each other: one of them has narrow leaves covered with dense white hairs, the other has broad leaves with sparse gray hairs. However, a thorough morphological study of their organs reveals much similarity.
One more species that has a lot in common with S. salviifolia is the American S. tristis Ait. Since Andersson's time (1859, 1868), most authors (including Schneider 1920a) mistakenly united this willow with S. sericea Marsh. and S. petiolaris Sm. However, Ball (1947) correctly placed S. tristis in sect. Vetrix (Capreae). The position of this species can be pinpointed even further. Together with S. aurita and S. salviifolia, S. tristis forms a natural, wholesome entity within subsect. Laeves of sect. Vetrix. As compared to the rest of Vetrix representatives (such as S. caprea L. or S. cinerea L.), the members of this group possess the following characters:
It is not easy to decide to which of the two related species S. salviifolia is closer. Its pronounced wood striation, the shape of buds and stipules, as well as male catkin morphology make it closely resemble S. aurita. In its leaf shape and pubescence as well as in morphology of developing fruiting catkins, S. salviifolia has much in common with S. tristis. As regards other characters, such as petiole length, leaf blade size, degree of stipule development, or catkin size, S. salviifolia occupies a position intermediate between S. aurita and S. tristis. In comparison with the other two species' characters, those of S. salviifolia can be presented as follows:
S. salviifolia
S. aurita and S. tristis
A tall shrub or a small tree. Pubescence on leaf undersides very much pronounced, mostly white.
Mostly tall or small shrubs. Pubescence on leaf undersides mostly gray, often disappearing in mature leaves.
S. salviifolia
S. aurita
Leaves 4 to 7 times as long as broad.
Leaves 1.5 to 3 times as long as broad.
Leaf margin mostly denticulate or entire.
Leaf margin mostly irregular, undulate, coarsely dentate.
Leaf apex acute or more or less obtuse, straight.
Leaf apex rounded or abruptly attenuating in a short, often crooked point.
S. salviifolia
S. tristis
Wood striae mostly pronounced, long, multiple.
Wood striae small, sparse.
Stipules broad, inequilateral, obtuse.
Stipules smaller, often nearly lanceolate and nearly equilateral, acute.
Floriferous buds broad deltoid-ovoid.
Floriferous buds narrower: up to oblong-ovoid.
Male catkins oblong-cylindric, 15-25 x 10-14 mm.
Male catkins oblong to nearly globose, 6-12 x 7-10 mm.
S. tristis is distributed in the eastern US from Massachusetts to northern Florida, westward to North Dakota and Nebraska.
In American literature S. humilis Marsh. is commonly positioned close to S. tristis. According to such researchers as Griggs (1905), Schneider (1920a), Argus (1964), S. humilis and S. tristis are just two extremes connected through a number of intermediate forms. This concept might be not right. Morphologic boundaries between species and diagnostic characters definitely require further elaboration, yet the treatment of S. tristis as a distinct species already appears to be sufficient. S. tristis differs from S. humilis morphologically, ecologically, and also geographically. S. humilis may be considered as yet another, fourth member of our species group. The majority of diagnostic characters for this group that have been described here above also fit S. humilis. At the same time, S. humilis, due to some of its characters, constitutes the link connecting the group of S. aurita-S. salviifolia-S. tristis with S. caprea.
Leaves of S. humilis, glabrous on the upper side, covered with spreading trichomes on the lower side, with their relatively long (4-12 mm) petioles, resemble S. caprea leaves.
Some samples of S. humilis with leafy branches generally look hardly different from small-leaf forms of S. caprea. This is particularly true for northern plants, the so-called var. keweenawensis Farwell, such as, for example, Bartram & Long 23745 from Nova Scotia, Garton 6305 from Ontario, or Jesup 37 from Massachusetts. In S. humilis anthers are larger than in S. tristis. Also, S. humilis has a larger range that is shifted more to the north in comparison with the range of S. tristis.
As it is obvious from the enclosed map, the entire group of species that we are talking about can be considered amphi-Atlantic. It is not represented anywhere in Asia (except for a tiny marginal part of S. aurita area in the Ural Mts., within the 500-mm isopluvial line.) This group is as well absent from western North America. Hulten (1958) has explained similar amphi-Atlantic distribution patterns by assuming connections in the past via Beringia and East Asia. However, in East Asia, which is generally so rich in species including primitive and relict groups of the genus Salix, not a single relative of the species in question has been found. If we accepted a possibility of direct trans-Atlantic Euro-American connections during the period from the beginning to mid-Neogen, then we could better explain the distribution patterns observed at present.
[List of observed herbarium specimens--S. salviifolia and S. tristis--omitted]
Trans-Atlantic connections of S. pedicellata Desf.
The author believes that S. pedicellata belongs to sect. Vetrix, subsect. Vulpinae together with such species as S. vulpina Anderss., S. silesiaca Willd., S. appendiculata Vill., S. caucasica Anderss. The close relation between the latter three species and S. pedicellata is apparent, while its connection with the Far Eastern S. vulpina is much less obvious. Together with some other Japanese-Korean willows, S. vulpina forms a tightly knit group within subsect. Vulpinae.
Differently from S. salviifolia, S. pedicellata is a typical Mediterranean species, according to its range. Its complete area lies within western Mediterranean area: Sicily, Sardinia, western Spain, and North Africa. It penetrates the eastern Mediterranean only in Lebanon and the adjacent parts of Turkey (and probably also on some of the Aegean Is. Subsp. canariensis (Chr. Smith) A. Skv. is distributed on Canary Is. and Madeira.
When looking for S. pedicellata relations among North American willows, we stop at S. lasiolepis Benth. This species is widespread in western North America from southern British Columbia to western Texas and northern Mexico. S. lasiolepis is particularly frequent in California, where it is one of the most common willows. Characters shared by S. lasiolepis and S. pedicellata can be summarized as follows:
It's important to note that S. pedicellata, as regards some of its characters (such as distribution across altitudes and latitudes, habit, floriferous bud morphology), is closer to S. lasiolepis than any of the European-Caucasian related species. As for differences between S. pedicellata and S. lasiolepis, they may be summarized as follows:
S. pedicellata
S. lasiolepis
pronounced wood striation under bark
wood striation absent
leaf margin often with large teeth (like in S. cinerea)
leaf-margin denticles small
leaf blades rather smooth and thin, upper side opaque
leaf blades more or less firm, coriaceous, their upper side smooth, more or less lustrous
bracts usually longer than broad, not truncate, with straight hairs, which overtop bract tips by 1.0-1.5 (-2.0) mm
bracts as broad as long or even broader, rounded or truncate at tips, with rather dense, somewhat wavy hairs, which overtop bract tips by 0.3-0.8 (-1.3) mm
stamen filaments free
stamen filaments often connate from base
capsule stipes 1.5-4.5 mm long
capsule stipes 0.8-2.0 mm long
style 0.2-0.4 mm long
style length varies from 0.2 to 0.8 mm
S. pedicellata ssp. canariensis is different from its continental counterpart in weaker wood striation, longer leaves with more lustrous upper surface, and shorter capsule stipes. Considering this character expression, we can place this subspecies even closer to S. lasiolepis. Besides, even within S. pedicellata sensu stricto one can find specimens in which wood striae are nearly absent, such as, for example, Desfontaines' specimen preserved in LE. On the other hand, in any large sample of S. lasiolepis, there may be found specimens with longer and straighter bract hairs.
In the American literature, S. lasiolepis is usually placed in sect. Cordatae Barr. The reason for that is, apparently, the similarity between S. lasiolepis and members of Cordatae in their large-sized, glabrous, stipitate, more or less pointed capsules. However, this type of capsules is not unique for Cordatae. Very similar capsules are also found in S. pedicellata, S. silesiaca, S. caucasica, the east-Asian S. vulpina, as well as in S. japonica Thunb. and S. shiraii Seemen and some members of sect. Helix. As for the rest of the characters, members of sect. Cordatae are different from S. pedicellata in nearly every other respect. The true members of sect. Cordatae, both American and Eurasian,[2] The Eurasian sect. Hastatae Kern. certainly has to be identified with Cordatae; the name Cordatae has the priority. all have either straight boreal or even sub-Arctic distribution. In southern parts of their areas, they are mostly restricted to montane forests or sub-Alpine and Alpine belt. The species of sect. Cordatae are drastically different from S. lasiolepis in the following characters:
Due to these significant differences, S. lasiolepis should be removed from sect. Cordatae and placed in sect. Vetrix, subsect. Vulpinae.
According to Schneider (1920b) and Ball (1961), a species closely related to S. lasiolepis is S. irrorata Anderss., which was also placed by these authors in sect. Cordatae. This opinion is completely unacceptable. In accordance with the structure of its vegetative organs as well as catkins, S. irrorata has even less in common with the species of Cordatae than S. lasiolepis. However, S. irrorata does not have much in common with sect. Vetrix, either. Perhaps we should consider placing S. irrorata together with S. geyeriana Anderss. and S. lemmonii Bebb.
S. tracyi described by Ball (1934) in my opinion is merely a poor (probably overtopped) form of S. lasiolepis with slenderer twigs and thinner, scarcely pubescent leaves. It flowers later and much less abundantly than S. lasiolepis. When the entire variability range of S. lasiolepis is taken into account, differences between S. lasiolepis and S. tracyi, as described by Ball (1934), appear not to be convincing enough.
Among the American willows, it is S. hookeriana Barr. that is the closest to S. lasiolepis. This was first noticed by Crovello (1968). Before that S. hookeriana had been placed together with S. lanata, S. barratiana, and S. alaxensis. In comparison with S. lasiolepis, S. hookeriana has thicker branches, larger buds, leaves, catkins, anthers, capsules, and stigmas; capsules are only very short-stipitate. All these differences, however, are purely quantitative; by no means they are contradicting the close affinity of the two species. Apparently, the S. lasiolepis-S. hookeriana group should be considered a special western-American entity within subsect. Vulpinae.
Due to lack of herbarium material, I could not reliably clarify the taxonomic value and position of S. piperi Bebb. It is quite possible that this is merely a form of S. hookeriana with weakly developed pubescence, which was described as a species similarly to S. tracyi, a form of S. lasiolepis.
East Asian members of subsect. Vulpinae -- S. vulpina and the closely related S. sieboldiana Blume and S. buergeriana Miq., in accordance with their morphological characteristics, cannot be considered a link between the groups of S. lasiolepis-S. hookeriana and S. pedicellata-S. caucasica. Similarly to the case of S. salviifolia, the hypothesis employing a possibility of direct trans-Atlantic early-Neogenic connections appears to be more convincing than the more complicated assumption of a connection via Beringia and Asia.
[List of observed herbarium specimens--S. pedicellata, S. lasiolepis, and S. hookeriana--omitted]
Andersson, N. J.1858. Salices boreali-americanae. -- Proceed. Amer. Acad. 4, Separatum: 1-32
Andersson, N. J.1868. Salix. In: De Candolle, A.P. Prodromus systematis naturalis 16 (2): 190-323
Argus, G. W.1964. Preliminary reports on the flora of Wisconsin 51. The genus Salix. -- Proceed. Wisconsin Acad. Sci. 53: 217-272
Ball, C. R.1934. New or little known West American willows. -- Univ. Calif. Publ. Bot. 17, N 14: 399-434
Ball, C.R.1947. Studying willows or making new sections in the genus Salix. -- Rhodora 49: 37-49
Ball, C.R.1961. Salix. In: Lundell, C.L., Flora of Texas 3, part 6: 369-392
Crovello, Th.G.1968. A numerical taxonomic study of the genus Salix, section Sitchensis -- Univ. Calif. Publ. Bot. 44: 1-61
Griggs, R. F.1905. The willows of Ohio -- Proceed. Ohio Acad. Sci. 4: 256-314
Hulten, E.1958. The Amphiatlantic plants. Stockholm
Hulten, E.1968. Flora of Alaska and neighboring territories. Stanford
Meusel, H., Jäger, E., and Weinert, E.1965. Vergleichende Chorologie der zentraleuropaischen Flora. Jena
Pereira Coutinho, A. X.1899. Subsidio para o estudo das Salicaceaes do Portugal. -- Bol. Soc. Broter. 16: 5-34
Schneider, C. K.1920a. Notes on American willows. IX -- J. Arnold Arbor. 2: 1-25
Schneider, C. K.1920b. Notes on American willows. XI -- J. Arnold Arbor. 2: 185-204
Skvortsov, A. K.1968. Ivy SSSR. Sistematicheskiy i geograficheskiy obzor [Willows of the USSR. Taxonomic and geographic revision.] Moscow: Nauka. 262 pp.
Skvortsov, A. K.1966. Salix. In: Arkticheskaya flora SSSR [Arctic Flora of the USSR] 5. Leningrad: Nauka. Pp. 7-118
Vicioso, C.1951. Salicaceas de Espana. Madrid

[1]   Specimens of the latter species from Alaska were identified by Hulten (1968) as S. arctica ssp. torulosa .
[2]   The Eurasian sect. Hastatae Kern. certainly has to be identified with Cordatae; the name Cordatae has the priority.

Translation I.Kadis
31 March 2007

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