American Rubus species in the Netherlands

American species of Rubus section Rubus were known from the Netherlands for many years. R. canadensis L. and R. allegheniensis (Porter) Porter have been found since several decades ago. Anne Troelstra came across some other species. With the help of Mark Widrlechner (IOWA State University) these could be identified. So we can add to the species mentioned above: R. alumnus L.H.Bailey, R. rosa L.H.Bailey and R. laudatus A.Berger. The occurrence of all these species is only as escaped plants, sometimes in a rather abundant vegetation, but none of them is invasive such as R. laudatus in Australia is.
All of these belong to the high bush brambles with suberect arching primocanes. R. allegheniensis, R. alumnus and R. rosa are members of the Alleghenienses, R. laudatus of the Arguti and R. canadensis of the Canadenses.

The rank of these infrageneric taxa is treated differently in Europe and in America. The American batologists conceive them as sections, while their European colleagues hold them for series. According to the European praxis the taxa are:
Series Alleghenienses (L.H.Bailey) A. Berger (1925), earlier than Krassowskaja (2000) and H.E. Weber  (later 2000) (= section Alleghenienses L.H. Bailey 1923).
Series Arguti (L.H.Bailey) A. Berger (1925) (= section Arguti L.H.Bailey 1923)
Series Canadenses (L.H.Bailey) A. Berger (1925), earlier than Krassowskaja (2000) and H.E. Weber  (later 2000) (= section Canadenses L.H. Bailey 1923).

The species can be distinguished from each other as follows:

1 a. Plant without any stipitate glands .... 2
  b. Plant with at least some short stipitate glands in the inflorescence (sometimes shorter than the hairs), often with many well visible stipitate glands .... 3
2 a. Leaves with a very long tip, almost glabrous downside, rather equally serrated; prickles few and weak .... R. canadensis
  b. Leaves short acuminate, downside soft hairy, coarsely serrate; prickles strong ....  R. laudatus
3 a. Only very short stipitate glands in the inflorescence .... R. rosa
  b. At least the pedicels with well visible glands ....  4
4 a. Inflorescence narrow, usually with few and weak prickles and not leafy to the apex; sepals smaller than 3x7 mm ....  R. allegheniensis
   b. Inflorescence broader, cylindric, usually with stronger compressed and curved prickles, leafy; sepals larger than 3x7 mm ....  R. alumnus

Photos and descriptions in Dutch can be found at:

R. canadensis: http://rubus-nederland.nl/nl/soorten/systematische-namenlijst/19-braam-genus-rubus-l/braam-subgenus-rubus/zwarte-braam-sectie-rubus/staande-braam-subsectie-rubus/spitsbraam-serie-canadenses-l-h-bailey-a-berger/192-r-canadensis-l

R. laudatus: http://rubus-nederland.nl/nl/soorten/systematische-namenlijst/74-braam-genus-rubus-l/braam-subgenus-rubus/zwarte-braam-sectie-rubus/staande-braam-subsectie-rubus/series-arguti-l-h-bailey-h-e-weber/373-r-laudatus-a-berger

R. rosa: http://rubus-nederland.nl/nl/soorten/systematische-namenlijst/24-braam-genus-rubus-l/braam-subgenus-rubus/zwarte-braam-sectie-rubus/staande-braam-subsectie-rubus/trosbraam-serie-alleghenienses-l-h-bailey-a-berger/390-r-rosa-l-h-bailey

R. allegheniensis: http://rubus-nederland.nl/nl/soorten/systematische-namenlijst/24-braam-genus-rubus-l/braam-subgenus-rubus/zwarte-braam-sectie-rubus/staande-braam-subsectie-rubus/trosbraam-serie-alleghenienses-l-h-bailey-a-berger/244-r-allegheniensis

R. alumnus: http://rubus-nederland.nl/nl/soorten/systematische-namenlijst/24-braam-genus-rubus-l/braam-subgenus-rubus/zwarte-braam-sectie-rubus/staande-braam-subsectie-rubus/trosbraam-serie-alleghenienses-l-h-bailey-a-berger/14-r-alumnus-bailey

Acknowledment:

Thanks to Mark Widrlechner for his support in the identification of the specimens.