Hybrid Mulleins
What are they?
The mulleins are famous - or perhaps infamous - for hybridizing with each other, seemingly at the drop of a hat. Native species are often loosely isolated by slight differences in habitat choice, but they can sometimes be found in close proximity to each other. However, an increasing number of species may be found as garden ornamentals and these may often escape into the wider countryside, from where they may come into contact with each other.
Where are they found?
Hybrids may appear anywhere that two species of mullein occur together. Hybrids involving non-native species can occur frequently in urban and suburban habitats.
Identification
Hybrid mullein are fairly frequent in occurence and may appear as odd individuals, or occasionally in small colonies. A hybrid might first be suspected if your mullein doesn't show all of the correct features normally associated with any one particular species, while they also tend to be mostly or completely sterile. Often, both parents can be found in the same area with a quick look around, but occasionally one or both parents may be absent or at least not apparent. Without the parents, a hybrid may well be unidentifiable for certain, so checking for parents is part of the identification process. As with the species mulleins, identification should include a check of: flower spike single or branched; leaf hairiness; attachment of the leaf bases to the stem; colour of hairs on the stamens. Note that some hybrids are rare enough that they have not officially been described and thus do not have a scientific name; such species are named here by their hybrid combination.
Verbascum x angulosum
(Dark x Hungarian Mullein) Has been recorded from Cambridgeshire and, more recently, West Norfolk, constituting the only British records. Look for the combination of the candelabra flower spike of Hungarian Mullein, together with at leaast some purple hairs on the stamens. Basal leaves typically have a purplish tinge to the petiole combined with a dense covering of branched hairs. The leaf base can be rather variable from more or less cordate to more or less cuneate.
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Verbascum x godronii
(Hoary x Great Mullein) Typically a fairly tall plant with a flower spike that has a few, usually short, side branches towards the base of the spike. Hairiness is like that of Great Mullein (i.e. not flocculating) while stem leaves are not decurrent (like those of Hoary).
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Verbascum x semialbum
(Great x Dark Mullein) Recorded a number of times across the region, where the parents occur together. Typically a fairly tall plant with a flower spike that is unbranched, or with few, short, side branches towards the base of the spike. The leaves are less hairy than those of Great Mullein and show the crenate margins and longer petioles of Dark Mullein. Typically the upper stamens bear purple hairs while the lower ones have white hairs and the anthers are all reniform.
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Verbascum x thapsi
(White x Great Mullein) Recorded a few times in Cambridgeshire. Usually rather stout plants with a variable appearance to the flower spike, but typically intermediate between the parents. Hairs on the calyx and anthers are like those of White Mullein but plants are mostly infertile and produce little (if any) seed.
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Verbascum pyramidatum x thapsus
Recorded a few times in Cambridgeshire, where the parents grow together. Typically stout plants with well-branched flower spikes like Caucasian Mullein, but with the decurrent stem leaves of Great Mullein.
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Verbascum pyramidatum x nigrum
Recorded a few times in Cambridgeshire and West Suffolk, where the parents grow together, but there have been no recent records. This hybrid typically closely resembles Caucasian Mullein but differs most noticeably in the flowers being carried in clusters of 2-5 at each node, rather than singly.
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White Nettle-leaved Mullein Verbascum chaixii var. album
Plants sold commercially as Verbascum chaixii var. album (and variations of that name) have white flowers, carried in a variably (often poorly-) branched spike. The stems and petioles are richly flushed with purple and the basal leaves have cordate bases. None of these features are typical of true Nettle-leaved Mullein, so it seems likely that these plants are hybrids, perhaps arising accidentally in cultivation through hybridisation with Dark Mullein.
Note: see also Nettle-leaved Mullein for the true species.
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