Fig 1.
Diagrams of major types of inflorescences in Cuscuta.
A. “Monogynella” type is a compound monochasial scorpioid cyme in which the main axes (e.g., I and II) superficially resemble thyrses. B. “Cuscuta” type is a simple scorpioid cyme, in this case with sessile flowers. B1. Simple cyme seen laterally (arrow indicates the direction of flower development). B2. Cyme seen from the top. C. “Grammica” type is also a compound monochasial scorpioid cyme, but with shorter axes. b = bract; ls = leaf scale; I, II, III indicate the order of axes.
Fig 2.
Development of “Monogynella” type of inflorescence.
A, B. The first inflorescence axis. A. Apical bud that grows vegetatively and generates lateral monochasial cymose axes. B. General view of first inflorescence axis. C–E. Progressive stages in the development of secondary axes. F, G. Simple scorpiod cymes developing on the secondary axes. H. More advanced stage in the development of the overall compound scorpioid cyme. I, II, III indicate axes of different orders. b = bracts; ls = leaf scale. Scale bars = 1 mm.
Fig 3.
Development of shoot system and “Cuscuta” type of inflorescence.
A–E. Sympodial development of exploratory shoot system. A–D. Axillary exploratory shoot. A. Apex of lateral exploratory shoot. B. Fragment of (primary) exploratory shoot showing axillary (secondary) developing exploratory shoot. C, D. Distal part of exploratory shoot from B. E. First two orders of exploratory shoots. F–I. Development of inflorescence. F. Incipient stage of flower primordia emerging at the base of series of axillary exploratory shoots (1, 2, 3, 4). G–I. Sessile flowers developing in zig-zag to form a simple scorpioid monochasial cyme (leaf scale removed from I). ls = leaf scale; lsp = leaf scale primordia; f = flower. Scale bars = 1 mm.
Fig 4.
Development of “Grammica” type of inflorescence.
A–D. Cuscuta gronovii. A1. Shoot. A2. Incipient stage of axillary inflorescence. B–D. Progressive stages in the development of compound monochasial scorpioid cyme resembling a panicle. E–J. Cuscuta campestris. Different stages of “glomeruliform-subglomeruliform” inflorescence development. K–M. “Rope” inflorescence of Cuscuta glomerata. K. General view of early stage. L. Flower primordia (indicated with arrows) emerging from haustorial stems. M. Developing flowers. ls = leaf scale; b = bract; Hs = haustorial stem; I, II, II, orders of axes; scale bars = 1 mm.
Fig 5.
Variation of inflorescence architecture in Cuscuta.
A, B. Subgenus Monogynella. A. Cuscuta lupuliformis. B. C. lehmanniana (photo by Vladimir Kolbintsev). C–E. Subgenus Cuscuta. C. C. planiflora. D. C. epithymum. E. C. babylonica (photo by Miguel García). F, G. Subgenus Pachystigma, “umbelliform-corymbiform” inflorescences. F. C. africana (photo by Miguel García). G. C. angulata (photo by Miguel García). H–P. Subgenus Grammica. H, I. “Umbelliform-corymbiform” inflorescences. H. C. sidarum. I. C. erosa (photo by Jillian Cowles). J–K. “Racemiform- paniculiform” inflorescences. J. C. corymbosa var. grandiflora. K. C. tinctoria var. floribunda. L, M. “Glomeruliform -subglomeruliform” inflorescences. L. C. volcanica. M. C. obtusiflora var. glandulosa. N. Flowers solitary or in fascicles, C. grandiflora. O. “Rope”, C. glomerata (photo by Richard Lutz). P. Mimetism of C. howelliana inflorescence developed inside the inflorescence of Eryngium castrense (Photo by Carol Witham).
Fig 6.
Summary of subgeneric character evolution hypotheses for the three main types of inflorescences using likelihood.
“Monogynella” type was suggested to be ancestral (proportional likelihood = 0.6962), followed by “Cuscuta” and “Grammica” types.
Fig 7.
Parsimony reconstruction of all the types of inflorescences, including the racemose analogies in subg.
Pachystigma and Grammica, revealed extensive convergent evolution in the latter subgenus.
Table 1.
Spearman’s correlation between all the inflorescence variables examined as well as pollen-ovule ratios, and fruit width.
Asterisk indicates significant p-values (p-value < 0.05).
Fig 8.
Principal component analysis (PCA) biplot of component 1 and component 2 using the inflorescence variables.
Colour groups show the different subgenera in Cuscuta.
Table 2.
Loadings for all the variables with the principal components.
Fig 9.
Correlation plots between components and reproductive traits.
A. Between component 1 and pollen-ovule ratios. Equation of the line of best fit: PO = 7.655 × (Comp 1)2 + 305.662 × (Comp 1) + 974.417. B. Between component 2 and pollen-ovule ratios. Equation of the line of best fit: PO = 54.93 × (Comp 2)5–80.28 × (Comp 2)4–358.95 × (Comp 2)3 + 448.34 × (Comp 2)2 + 162.83 × (Comp 2) + 765.47. C. Between component 1 and fruit width. D. Equation of the line of best fit, Fruit width B = 0.3327 × (Comp 1) + 2.7887. Equation of the line of best fit, fruit width B = −0.07643 × (Comp 2) + 2.78871.
Table 3.
Spearman’s correlation between principal component 1 and principal component 2 with pollen-ovule ratios, and fruit width.
Asterisk indicates significant p-values (p-value < 0.05).
Fig 10.
Boxplot of fruit width for DE, DE+IrA, IN, and IN+IrB modes of dehiscence (3 groups were removed as they had 3 taxa or less).
Boxes show the middle 50% of component 1 values for the modes of dehiscence, horizontal lines in the boxes show the median, circles are outliers, and the whiskers show the minimum and maximum values. Significant differences were noted for at least two of the groups of dehiscence examined. Pairwise comparisons using Wilcoxon rank sum test revealed significant differences between IN and DE (p-value = 0.033), and IN+IrB and IN (p-value = 0.033).