Euphrasia

Abstract: (1) Detailed demographic observations were made in permanent quadrats on three hemiparasitic summer annuals (Euphrasia pseudokerneri, E. nemorosa and Rhinanthus minor) and two strict biennials (Linum catharticum and Gentianella amarella) at three chalk grassland sites in England from April 1979 to October 1981. All species flowered in the autumn and germinated in the spring. (2) Variation over three years in the exact time of germination was correlated with temperature in E. pseudokerneri and Gentianella. Linum germinated at the same time every year, even at sites in different countries; daylength may be a controlling factor. (3) In 1981, early-germinating seedlings had lower survival to flowering in Linum and Gentianella, but in E. pseudokerneri germination date had no effect on survival. (4) In summer 1980, both biennials had a sizeable seed bank (600-2500 m-2), but E. pseudokerneri had virtually none. For all three species, most seeds which germinate apparently do so in the first spring after seedfall. In the field, 14% of seeds sown in autumn 1980 germinated the following spring for Euphrasia, 24% for Linum and 30% for Gentianella. (5) Survival from germination to flowering varied significantly between years by as much as 30-fold. There was less difference between years in the pattern of mortality through the growing season. Survival to flowering ranged from 43% to 0-8% in the annuals and from 12% to 6% in the biennials. (6) Many flowering plants (up to 38%) and many flowers (up to 46%) set no seed. Seed outputs per fruiting plant were very low (10-25 for the Euphrasia spp. and Linum, and 3090 for Rhinanthus and Gentianella), and varied between sites and years. Estimates of seed output were an order of magnitude lower than those of Salisbury (1942). (7) Both Linum and Gentianella were strict biennials (flowering only in the second year) in Cambridgeshire. Both may have annual forms elsewhere but theoretical considerations suggest that the chalk grassland sites are so low in nutrients and so densely vegetated that Linum and Gentianella cannot reach reproductive size in one year. Work on Linum in Holland, where annual forms are found, supports this view.

Abstract: Recent information is reviewed on the population biology and habitat relations of some hemiparasitic Scrophulariaceae (Pedicularis, Rhinanthus, Melampyrum, Odontites, Euphrasia and Parentucellia species). The species occur in a wide range of habitats; they are not host specific, except perhaps for Melampyrum sylvaticum in field conditions. A wide range of hosts may be parasitized, but a high inter- and intra-specific variation of ‘host quality’ was observed. There is also intra-specific variation of the parasitic ability of the parasites. These may reduce the development of their hosts, and so may affect the composition of a vegetation.

Abstract: Previous workers found that Euphrasia could be brought to maturity in cultivation whether supplied with a host-plant or not (though better growth was obtained with a host than without), and found also that a wide variety of annual and perennial herbs could act as hosts. The present paper describes chiefly cultures in clay pots, into which the Euphrasias were transplanted as seedlings. Usually growth was better when a host was provided than when it was not, but growth without a host was better than that obtained by previous workers. The development of some plants without a host was much affected by a difference of soil composi­ tion. A spurt of growth some weeks after planting with a host was taken to indicate parasitic establishment on the host, and the shorter the distance between the Euphrasia and its host the sooner establishment occurred. Euphrasias grown with certain Leguminosae were particularly vigorous and showed symptoms of a good nitrogen supply. Some severely retarded Euphrasia plants were probably being parasitized by their neighbours. Euphrasias sometimes flowered very early, beginning at a very low node; this appeared to be caused by unusually high temperatures. The early-flowering species were particularly frequently affected in this way, which made it difficult to raise normal plants of these species. Deaths of young Euphrasia plants took place chiefly in cold, dull weather, but were reduced by watering sparingly. Cultures of various Euphrasia species with various hosts showed that certain hosts were good, and that others were bad or probably bad. There were indications of a difference between E. pseudokerneri and E. anglica in their growth on the same hosts. Different populations of the same Euphrasia species sometimes differed in their host-reactions. The host affected percentage establishment, mortality and vigour of the Euphrasias. For cultivation in the open ground Euphrasia plants and hosts were planted in bituminized paper pots, which were embedded in the ground. Very vigorous growth was obtained in this way, using Plantago lanceo/ata as a host-plant. The parasitic habit is probably not responsible for the taxonomic complexity of Euphrasia, but may be connected with its gregariousness in nature. PREVIOUS WORK