Taraxacum dooguei and T. dudmanianum (Asteraceae)-two new species from Britain and Ireland

Two new species of Taraxacum are described: T. dooguei A.J. Richards, a section Celtica species from Ireland related to T. pietii-oosterveldii, and T. dudmanianum A.J. Richards, a section Taraxacum species from Britain and Ireland previously incorrectly recorded as T. aberrans. Notes are given on their ecology and distribution.


Introduction
While preparing the forthcoming BSBI Field Handbook to British and Irish Dandelions (Richards, 2021), it became clear that it was necessary to describe two new species. These are described and discussed below.
Later in 2015, and again in 2018, Doogue collected similar but better material from Saint's Island, Lough Ree (N0756) (v.c.H24, Co. Longford), and in 2019 from the Great Heath of Maryboro (N5301) in Laois (v.c.H14). This was found to differ from T. anglicum in several characteristics, notably by having more pairs of lateral leaf-lobes, shorter ligules, an absence of pollen, narrower exterior bracts and larger achenes. It was originally given the workname 'T. turloughense', but is now being described as a new species T. dooguei in section Celtica A.J. Richards. Its closest relative is considered to be T. pietii-oosterveldii H. Øllg., a species which had not been described in 2015, but is currently known to be widespread and frequent through much of Ireland and west Wales in wet habitats, and is also found rarely, perhaps introduced, in England, Netherlands and Denmark. T. dooguei and T. pietiioosterveldii are relatives of T. nordstedtii Dahlst., sometimes distinguished by Netherlands botanists as central to an informal subgroup 'Frugalia'.
In common with other members of the T. nordstedtii group, T. dooguei has short ligules with a solid brownish-purple stripe, which scarcely exceed the inner bracts. Like T. pietii-oosterveldii, pollen is absent and the stigma branches dry blackish. It differs from T. pietii-oosterveldii, with which it sometimes occurs, principally by lacking the abruptly, even acutely, angled distal margin to the lateral leaf-lobes. In fact the lateral lobe distal margins are usually straight, unlike those of both T. pietii-oosterveldii and T. nordstedtii, so that the reflexed leaf lobes appear sagittate. The achenes are larger than those of T. nordstedtii, but similar in size to those of T. pietii-oosterveldii although more rugose throughout and with a shorter cone. Unlike T. pietii-oosterveldii the leaves sometimes have small black spots on the upper surface. Both T. pietii-oosterveldii and T. dooguei have narrower exterior bracts than those of T. nordstedtii, darker stigmas, and, unlike the latter species, the bracts are not pruinose. T. olgae, endemic to the Solway Firth districts of England and Scotland, is similar to T. dooguei in many ways, and shares a tendency to produce small scattered black spots on the upper leaf surface, but has much smaller achenes and fewer pairs of lateral leaf lobes. The subsagittate leaves of T. dooguei are distinctive and reminiscent of T. akteum Hagend., Soest & Zevenb. which is not a member of the T. nordstedtii alliance and has spreading exterior bracts and longer ligules. British plants originally identified with T. texelense Hagend., Soest & Zevenb are now considered to be T. akteum.
Taraxacum dooguei grows in and at the margins of permanently or seasonally wet highly calcareous lake margins where it is often accompanied by the section Palustria species T. amarellum and T. webbii A.J. Richards. At present it is known from five sites in central Ireland (Fig. 2) . 3).

Figure 3. Holotype of T. dudmanianum (NMW). Image: Richard Pryce.
This section Taraxacum (previously known as section Ruderalia Kirschner, H. Øllg. & Štĕpánek) taxon has been known in Britain and Ireland as T. aberrans Hagend., Soest & Zevenb. (1974) for four decades, and before that as T. caudatulum Dahlst. (Dudman & Richards, 1997). However, it is clear from the type description and figures from the website taraxacumnederland.nl that it is not T. aberrans. It appears to be identical to the taraxacumnederland.nl figures of T. breviflorum Dahlst. (Fig. 4).
However, online representations of the lectotype of T. breviflorum (S) are of another taxon. The British and Irish plant is familiar, widespread and not uncommon in our islands, but at present we have no valid name for it. Although it may well be recognized elsewhere in Europe, I have not been able to find its counterpart after widespread enquiries, although clearly it also occurs in the Netherlands without a valid name. Amongst recognised British and Irish species, it comes close to T. pseudoretroflexum M.P. Christ. in section Taraxacum. It differs principally by the notably claw-shaped (half-recoiled) exterior bracts, and the larger, more rounded terminal leaf lobes to the inner leaves.  Taraxacum dudmanianum has winged petioles which are pink on the inner leaves and whitish on the outer leaves (Fig. 6), and heterophyllous leaves in which the terminal leaf-lobe is much larger in inner leaves than outer leaves at flowering time (Figs. 3 and 5). This places it in the informal group Ekmania of section Taraxacum in Richards (2021). In addition, like the familiar and common T. ekmanii Dahlst., it has pale green, rather flaccid leaves. However, T. dudmanianum has a short apiculate apex to the large terminal lobes to the inner leaves, and lacks the semi-lunate, somewhat sigmoid lateral lobes of the outer leaves of T. ekmanii.
Distinctively, the outer exterior bracts have a semi-recoiled posture to give a talonlike shape (Fig. 7), an unusual feature which is best known in the otherwise very dissimilar T. polyodon Dahlst. This feature is the best discriminant in comparison with T. pseudoretroflexum, as noted above, although the two species differ in leafshape.    Fig. 8). It apparently occurs in the Netherlands, but as yet its distribution outside Britain and Ireland is uncertain. Like most members of section Taraxacum it favours anthropogenic habitats, road-verges and banks, hedge-rows, gardens and waste-places, although it may also occur in open semi-natural habitats.