Hieracium monstrosum Hyl. als ingeburgerde graszaadneofyt in enkele Gelderse landgoed- en kasteelparken

In 1926, Zahn described Hieracium murorum subsp. henrardii in van Soest’s (1926) revision of the genus in the Netherlands on the basis of one single collection made by J.Th. Henrard near Ampsen (Province of Gelderland) in the autumn of 1908. Since the plants seem to be very a-typically developed, like often in late flowering specimens of Hieracium sect. Hieracium, it appeared very unlikely that the identity of the plants would ever be revealed. Several attempts to search for plants of this section in the direct vicinity of Ampsen were unsuccessful and it was believed that Henrard’s hawkweed had disappeared. However, between 2007 and 2012 we collected several plants in a somewhat wider region around Ampsen (i.e. Castle Hackfort in 2007 and the estate Kieftskamp near Linde in 2012) which, after a thorough study of the material, have been identified with certainty to belong to the same taxon. Two specimens in Van Soest's herbarium in L that were collected near Castle De Wildenborg and the estate Kieftskamp in 1937 proved to belong to this taxon as well. All plants have the typical long petioles found in Hieracium murorum subsp. henrardii and have similar (rather peculiar) teeth at the leaf margins. After an additional and thorough search in L, we located two more herbarium specimens that belong to this taxon. They were collected by D. Douwes near Huize Zelle (Province of Gelderland) in 1981 and Linde in 1982. It should be noted that P. Heukels identified Douwes' plant from Huize Zelle already in 1981 as H. murorum subsp. henrardii. Several unidentified specimens of Hieracium sect. Hieracium were send on loan to Torbjörn Tyler (Lund, Sweden), amongst which one plant collected in the park of Palace Het Loo near Apeldoorn. Tyler identified this plant as Hieracium monstrosum, a species described by Hylander based on material from the park of the Mälsåker estate near Ytterselö in 1943 and only known from the type locality and the park of Castle Tynnelsö near Överselö, both in the Province of Södermanland, Sweden. After examination, we can only conclude that the specimen from Het Loo belongs to the same taxon as those from Ampsen, the Kieftskamp, De Wildenborgh, Huize Zelle, and Linde. Consequently, H. monstrosum and H. murorum subsp. henrardii are conspecific. Just like in Sweden, H. monstrosum in Gelderland is found in castle and estate parks and it probably was introduced between 1750 and 1935 as a contamination of grass seeds ('wood lawn neophyte'). An extensive description and photos of H. monstrosum are given to facilitate its future recognition.