Rare Plant Register
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1 BSBI RARE PLANT REGISTER Berkshire & South Oxfordshire V.C. 22 MICHAEL J. CRAWLEY FRS UPDATED APRIL 2005 2 Symbols and conventions The Latin binomial (from Stace, 1997) appears on the left of the first line in bold, followed by the authority in Roman font and the English Name in italics. Names on subsequent lines in Roman font are synonyms (including names that appear in Druce’s (1897) or Bowen’s (1964) Flora of Berkshire that are different from the name of the same species in Stace). At the right hand side of the first line is a set of symbols showing - status (if non-native) - growth form - flowering time - trend in abundance (if any) The status is one of three categories: if the plant arrived in Britain after the last ice age without the direct help of humans it is defined as a native, and there is no symbol in this position. If the archaeological or documentary evidence indicates that a plant was brought to Berkshire intentionally of unintentionally by people, then that species is an alien. The alien species are in two categories ● neophytes ○ archaeophytes Neophytes are aliens that were introduced by people in recent times (post-1500 by convention) and for which we typically have precise dates for their first British and first Berkshire records. Neophytes may be naturalized (forming self-replacing populations) or casual (relying on repeated introduction). Archaeophytes are naturalized aliens that were carried about by people in pre-historic times, either intentionally for their utility, or unintentionally as contaminants of crop seeds. Archaeophytes were typically classified as natives in older floras. Absence of ○ or ● at the start of the list of traits means ‘native’ (i.e. not introduced by people). Growth form describes the structure and life history of the plant. The broad categories are woody plants, herbaceous perennials and annuals, but here I have used the rather more extended system devised by the famous Danish ecologist Raunkiaer (as used in Clapham, Tutin and Warburg’s Flora of the British Isles). The system is based on the position of the perennating organs (i.e. the location of the buds during the unfavourable season). It is unfortunate that Raunkiaer used such grandiose language for the names of his life forms, but the system is highly practical and has stood the test of time. Woody plants (phanerophytes) are characterized by the fact that they hold their perennating buds aloft, exposed to the winds and winter weather; trees are mega-phanerophytes and dwarf shrubs are nano-phanerophytes. Bulbs and rhizomes are two examples of geophytes where the perennating buds are held underground during the unfavourable season. Cushion-forming perennials are known as chamaephytes. A great many herbaceous perennials have long-lived root systems, but their shoot systems die back to the ground each autumn, and their perennating buds are held close to the soil surface (these are the hemicryptophytes). Annual species have no perennating organs, but survive the unfavourable season as seeds (these are known as therophytes, and their buds are embryonic). Flowering time is shown as the number of the month in which the species is first likely to be seen in flower in the year (4 = April, 6 = June, etc.). There has been a trend towards earlier flowering of early-season species in recent years, but summer flowering species have shown no such trend. Species that flower only once in the year (like oaks or bluebells) will typically not be found in flower any later than one month after the first flowering date. For repeat flowering species, however, the duration of flowering is highly variable from year to year depending on the vagaries of summer droughts, early autumn frosts, and so on. I have made no attempt to indicate the last month of flowering, but for many repeat flowering species, it is October (when the first serious air frosts are likely to occur). In mild autumns, however, many species continue flowering until after Christmas time. The final symbol in the list indicates trends in abundance of the species in Berkshire. Such trends are notoriously difficult to estimate from historical sources, because authors were so variable from one to the other, and so inconsistent personally, in their assessments of plant abundance. When in doubt, I have omitted any indication of trend. Species that have clearly increased or clearly decreased in the last 100 years are shown like this: ↑ increasing in abundance ↓ declining in abundance † extinct in Berkshire Absence of ↑ (increasing) or ↓ (declining) from the end of the list means ‘stable’ in distribution and abundance. Note that extinction is an hypothesis rather than a fact. We suppose that a species is extinct until we rediscover the plant in one of its former habitats, or find it growing in a new place. It may be that some of the species that I have marked as declining are, in fact, already extinct. We really need to monitor all of the declining species on a regular basis and visit all of the former sites of all the species that are thought to be extinct (this is what is proposed under the new scheme proposed by the Botanical Society of the British Isles to maintain County Rare Plants Registers). What is obvious is that if we don’t look for these plants, then they are certain to stay extinct. One of the great joys of field botanizing is to rediscover a species that was thought to be extinct (see, for example, Lythrum hyssopifolium). Some examples follow: th 6 3 This is read “native annual, flowering from June, stable in abundance”, whereas ○ hyd 5 ↑ is read “archaeophyte aquatic, flowering from May, increasing in abundance”, and ● n 3 † is read “introduced shrub, flowering from March, extinct” Order within the text First, the habitats are listed, in order of importance. Next, indications of distribution and abundance are given (e.g. “widespread and common”, or “local and rare”). Where appropriate, tips on identification are given. Finally, a list is given of the plant communities in which the plant grows in Berkshire (NVC stands for National Vegetation Classification). The system is incomplete at present, and some common plants have no home under the NVC (e.g. Veronica serpyllifolia). Distribution details are given under four headings: within Silwood Park, with the Ascot District, in East Berks and in West Berks (below). For species that have shown a trend in abundance, downwards or upwards, I have given all of Druce’s and Bowen’s sites. The rationale is that by revisiting these sites with a specific species in mind we might rediscover some of them. Thus, within East or West Berks, the sites known to Druce in 1897 are listed first. After a full stop, the sites known to Bowen are listed; this may or may not involve repetition of Druce’s records, depending upon whether a species was still present at a site in Bowen’s time. Finally, after a second full stop, the recent (and by implication current) records are given; unless stated otherwise these are by M.J. Crawley. Numbers appearing in square brackets are grid references. At the end of the list, the 10km squares in which the species was recorded during field work for Atlas 2000 are listed. Post-1999 records do not appear in this list, but are explained in the text. Silwood Park: Records refer to the study period 1979-2004. The place names within Silwood Park refer to roughly 1 ha areas. Ascot: This section is mentioned only when a species is rare or absent in Silwood Park. The district comprises all of the v.c. 22 part of [96], including the southern-western part of Virginia Water plus the villages of Sunninghill, Sunningdale, Ascot and South Ascot. The easternmost 1km strip of [86] is included, along with the southernmost 2km strip of [97]. Historically, the district was well botanized, especially Sunningwell Bog to the south of The Wells, and Ascot Heath racecourse because of botanists spending time at the homes of local gentry. East Berks: The convention for presenting the 10 km distribution data follows the standard practice for giving grid references: eastings first, then northings. Thus, the squares that make up East Berks are [76], [77], [78], [86], [87], [88], [96], [97], [98] This kind of ubiquitous distribution would be written as Atlas 2000: all squares for brevity. When the species is found in most squares, the convention is to write Atlas 2000: all squares except [96] Note that in the case of “all squares except” I do not mention [98] because such a tiny part of it occurs in v.c.22, and absence from such a small area would be uninformative. The same convention is adopted for squares [27] and [30] in West Berks. West Berks: There is a slight complication in the numbering system for the 10km squares in West Berks, because two of them, [40] and [50], are in a different 100km square from all the others (SP rather than SU). To maintain the convention that the squares are presented from south to north at each 10km eastward, the numbering looks like this: [48], [49], [40], [59], [50] for a species that occurs throughout the Northern Loop (the oolitic limestone district to the south of Oxford). The sequence of families, genera within families and species within genera follows Stace (1997). LYCOPODIACEAE Huperzia selago (L.) Bernh. ex Schrank and Mart. Fir Clubmoss chh 6 † 4 Lycopodium selago L. Extinct bog plant. A rare component of the Erica tetralix-Sphagnum compactum wet heath. NVC: M 16 Its loss may have been due to drainage and habitat destruction, but it might be that long-term warming and reduced rainfall caused its demise, because several other species from Erica tetralix wet heath have declined, even in well managed nature reserves (e.g.