A review of the genus Rhipidoglossum Schltr

The large number of African orchids belonging to the group Monopodiales, the so-called ”Angraecoid Orchids“, constitute a puzzling assemblage of which the main lines of classification are still uncertain. Several well-defined minor groups can, however, be readily distinguished, the most striking of which are such genera as Cyrtorchis Schltr., Aerangis Schltr. (sensu stricto) and Tridactyle Schltr. Among the less welldefined but nevertheless reasonably natural groupings is the genus Rhipidoglossum. This genus was described by Schlechter in his comprehensive treatment and revision of the Angraecoid orchids in 1918. He separated four genera, including Rhipidoglossum, from the remainder on account of the presence of a foot to the column. This character, which appears to be of value in the delimitation of Asiatic genera belonging to the Monopodiales, is, however, of less use in classifying the African genera. Several pairs of closely allied species occur in which one species is with and the other without a foot to the column. On the whole those genera constantly possessing a column-foot can he easily characterised by other more obvious features. Rhipidoglossum, on the other hand, is clearly very closely allied to Diaphananthe in which the column foot is absent or very weakly developed. Indeed the theoretical delimitation of these two genera rests on the presence or absence of a callus in the mouth of the spur, the callus being absent in Rhipidoglossum. At the same time the two genera show different ranges of variation in habit and in floral structure, although the species at the various points of contact closely resemble some of those in the other genus. For instance, the stem is usually elongated in Rhipidoglossum whereas it is short with a rosette type of growth in Diaphananthe. D. bidens, however, which is typical in other respects, has much elongated stems. There is, on the other hand, a tendency towards shortening of the stem in some species of Rhipidoglossum. Secondly, in Diaphananthe the pollinia, although always provided with distinct stipites, usually share a common viscidium. There are also, however, a number of species in which two separate viscidia are found, this feature being general in Rhipidoglossum. The column in the two genera is very similar, and the rostellum is of the same general type

Detection of delayed density dependence in an orchid population

1 Annual censuses of Orchis morio (green-winged orchid) flowering spikes have been taken over a 27-year period in a replicated factorial experiment on the effects of fertilizer application. Census data, combined by block or treatment, were used in time-series analyses to test for density dependence. 2 Partial autocorrelation functions revealed the importance of positive correlations at lag 1 and negative correlations at lag 5. Stepwise multiple regressions provided evidence of delayed density dependence, again with a delay of about 5 years, with no evidence of direct (first-order) density dependence. 3 First-order autocorrelations and delayed density dependence were considered in the light of the known stage structure and generation time of the plant and the possibility of density dependence at different points in the life history. 4 Model structure affects the detection of density dependence, increasing the propensity for type I errors

The alien terrestrial invertebrate fauna of the High Arctic archipelago of Svalbard: potential implications for the native flora and fauna

Experience from the Antarctic indicates that the establishment of alien species may have significant negative effects on native flora and fauna in polar regions and is considered to be amongst the greatest threats to biodiversity. But, there have been few similar studies from the Arctic. Although the terrestrial invertebrate inventory of the Svalbard Archipelago is amongst the most complete for any region of the Arctic, no consideration has yet been made of alien terrestrial invertebrate species, their invasiveness tendencies, threat to the native biology or their route of entry. Such baseline information is critical for appropriate management strategies. Fifteen alien invertebrate species have established in the Svalbard environment, many of which have been introduced via imported soils. Biosecurity legislation now prohibits such activities. None of the recorded established aliens yet show invasive tendencies but some may have locally negative effects. Ten species are considered to be vagrants and a further seven are classified as observations. Vagrants and the observations are not believed to be able to establish in the current tundra environment. The high connectivity of Svalbard has facilitated natural dispersal processes and may explain why few alien species are recorded compared to isolated islands in the maritime Antarctic. The vagrant species observed are conspicuous Lepidoptera, implying that less evident vagrant species are also arriving regularly. Projected climate change may enable vagrant species to establish, with results that are difficult to foresee