Short Corolla Tube Research Articles

A new species of Canthium (Rubiaceae) from southern Natal and Pondoland

Canthium vanwykii Tilney & Kok, a fairly common shrub or small tree endemic to the sandstone region of southern Natal/Pondoland is described. The species is mainly confined to forest margins and can readily be distinguished from the other southern African species of Canthium Lam. s . str . chiefly by a combination of inflorescence and floral characters. It appears to be most closely related to C . ciliatum (Eckl. & Zeyh.) Kuntze from which it differs in several of these and other features. Diagnostic characters for C . vanwykii include the many-flowered inflorescences, essentially pentamerous flowers, a relatively short and funnel-shaped corolla tube, corolla lobes which exceed the length of the corolla tube and distinctly petiolate and usually widely ovate to widely elliptic leaves with pubescence largely restricted to the midrib, petiole, and principal lateral veins.

Floral Resource Sharing by Bumblebees and Hummingbirds in Pedicularis (Scrophulariaceae) Pollination

MACIOR, L. W. (Dept. Biol., Univ. Akron, Akron, OH 44325) Floral resource sharing by bumblebees and hummingbirds in Pedicularis (Scrophulariaceae) pollination. Bull. Torrey Bot. Club 113:101-109. 1986.-Pedicularis densiflora in California was found to be animal pollinator dependent. Younger flowers with short corolla tubes were pollinated by short-tongued Bombus edwardsii workers foraging primarily for nectar, while older flowers with deep tubes were pollinated by nectar-foraging Anna and rufous hummingbirds. Scarlet corollas apparently attract birds, while magenta calyces and floral bracts with highly ultraviolet reflective hairs attract bumblebees. Nectar concentration (sucrose equivalents) varied from 15.0 to 24.5%; only fructose and sucrose were present. Cinematographic and stereophotographic records indicated that the flowers are pollinated only nototribically by birds and insects. Of 83 corbicular pollen loads from 193 B. edwardsii worker pollinators, 55% contained P. densiflora pollen, and 60% contained pollen of Dodecatheon hendersonii, suggesting that these two plants share pollinators by synchronously supplying complementary resources in the same plant community. The earlier blooming Arctostaphylos did not effectively deflect Bombus pollinators from P. densifora, but observations on a community including synchronously blooming Arctostaphylos and Pd. aurantiaca, a subspecies with variably colored flowers, indicated that Arctostaphylos preferentially attracted Bombus pollinators with hummingbirds exclusively pollinating Pd. aurantiaca. Pedicularis densiflora is considered a species in transition between two pollination syndromes, influenced by the biotic and physical circumstances of the environment.

Corolla tube formation in six species of apocynaceae

Corolla tube formation inTrachelospermum asiaticum, Nerium indicum var.leucanthum, Anodendrom affine, Vinca major, Catharanthus roseus andAmsonia elliptica was investigated anatomically.The corolla tube formation among these species is basically similar. The bases of petal primordia extend laterally to the interprimordial regions, the upward growth occurrig at those regions just beside the petal bases. The extending petal bases connect with each other at the bases of the abaxial side of stamen primordia in the early stage of the corolla development. The upward growth at the coonnected regions results in the formation of a short corolla tube but is weakened rapidly. At the stage of the mutual connection of petal bases, a common base of petal and stamen primordia is initiated. This common base develops into the lower portion of the corolla tube, i.e. the portion below the stamen insertion.In a relatively late stage, adjacent margins, of the corolla lobes fuse postgenitally at their lower portions, resulting in the formation of almost all of the upper portion of the corolla tube.The corona inNerium andVinca is initiated by the active adaxial growth of the upper portion of the corolla tube.

Resource Partitioning in Bumblebees: The Significance of Differences in Proboscis Length

The resource utilization by nine species of bumblebees in a subarctic community was studied by analysing the distribution of the depths of the corolla tubes of the visited flower species. When measured in this way, the food niches of the bumblebee species showed a wide overlap. Species with a long proboscis could use flowers with short corolla tubes for feeding, whereas the reverse was rare. We postulate that foraging efficiency is maximal when the proboscis length of a species corresponds to the corolla tube depth of the flower visited. An analysis of published data supports this hypothesis. The paucity of plant species with deep corolla tubes thus explains the small number and low abundance of bumblebee species with long proboscis. The continuously changing pattern of corolla tube depths due to the seasonal succession of plant species facilitates the coexistence of many bumblebee species in a community in spite of small differences in proboscis length.

The effect of proboscis and corolla tube lengths on patterns and rates of flower visitation by bumblebees.

The rates at which bumblebees of different proboscis lengths forage on flowers of a series of corolla tube lengths were determined. The results indicate significant correlations between proboscis length and time spent by bees on flowers. Bumblebees of long proboscis length can forage significantly faster than bees of shorter proboscis length on flowers with long corolla tubes. There is also evidence which suggests that bumblebees of short proboscis length prefer and are more efficient on short corolla tubes. These results support the use of proboscis length as a morphological indicator of resource utilization in bumblebees.

A Revision of the Justicia Insularis-Striata Complex (Acanthaceae)

The complex is divided into two species, Justicia schimperi and J. striata. The former is distinguished by its long slender corolla tube which exceeds the length of the lip and by its rich pink flowers; the latter by its short corolla tube which is equalled or exceeded by the lip and by its usually cream-coloured flowers. J. insularis is reduced to a subspecies of 3. striata, intergrading with J. schimperi in south-eastern Nigeria. J. schimperi is divided into two subspecies, one of which comprises two varieties, while J. striata is divided into four subspecies, one of which comprises two varieties. Variation of J. schimperi is discussed in the light of cultivation and hybridization experiments, and chromosome numbers are given for two subspecies of this species.

Length of tongue in a honey bee in relation to the pollination of red clover

SummaryRed clover florets are generally longer than a honey bee's tongue. Original data are submitted showing that honey bees can reach to a depth of 7 mm into the corolla tube of a red clover floret. The importance of this figure is discussed in relation to breeding bees with longer tongues and the breeding of red clover with shorter corolla tubes. Breeding a variety of red clover with more nectar so that honey bees can reach it is considered to be the best solution and would produce an increase in yield of both seed and honey.

Corolla Tube Length Studies in Red Clover1

The relationship between corolla tube length and seed production was studied in two long corolla tube strains and two short corolla tube strains of red clover. Although the strains differed significantly in mean corolla tube length, the short corolla did not appear to offer any advantage for increased seed production. Because it was thought that strain differences other than corolla tube length might have been involved in the above mentioned studies, the relationships between corolla tube length, number of florets per head, seeds per head, and percentage of florets setting seed in segregating populations derived from crosses between long and short corolla tube strains were studied. In the entire population neither number of seeds per head nor percentage seed set was significantly correlated with corolla tube length. The only significant correlation was between florets per head and seed setting percentage, the r value being + 0.339. Crosses between plants of varying corolla tube lengths were made to study the relationship between the corolla tube length of parental plants and that of their progenies. Sixteen plants in each of 17 families were studied. There was a highly significant correlation between the mean corolla tube length of the parents and that of their progenies, the r value being .84. Long corolla tube tended to be dominant or partially dominant over short. One family was selected for further study of corolla tube length in F2 and backcross populations. The F2 populations derived from long X long, medium X medium, and short X short corolla tube F1 plants were significantly different in mean corolla tube length. It was possible to shift the mean corolla tube length of both the F2 and backcross populations by selecting long or short corolla tube F1 plants to produce these populations. The mean corolla tube length of all backcrosses to the long corolla tube parent was 7.55 mm and of all backcrosses to the short parent was 6.81 mm. The weights of the individual plants in the F2 and backcross populations were determined at the end of the growing season. There was a highly significant difference among the mean plant weights of the various populations. All of the backcross populations from the long corolla tube Emerson parent had a significantly higher mean plant weight than the backcross populations from the short corolla tube Zofka parent. The average plant weight of all backcross populations involving the Emerson parent was 27.02 grams and of all backcrosses involving the Zofka parent was 20.44 grams. The F2 population derived from the two short corolla tube F1 plants was significantly lower in mean plant weight than the F2's derived from the medium and long corolla tube F1 plants. In the backcrosses to both parents, the populations involving the short F1 plants also were lower in mean plant weight than the populations involving the medium or long F1 plants. The correlation between plant weight and corolla tube length on an individual plant basis gave an r value of +0.27, which was highly significant. The correlation between the mean plant weight and mean corolla tube length of the populations gave an r value of +0.83. This indicated that genes for corolla tube length apparently were associated with genes for the expression of general vigor.