| Life form |
Perennial, hemiparasitic vines (Heide-Jørgensen 2008Heide-Jørgensen H (2008) Parasitic flowering plants. Brill., Tennakoon et al. 2016Tennakoon KU, Rosli R & Le QV (2016) Biology of aerial parasitic vines in Brunei Darussalam: Cuscuta and Cassytha. Scientia Bruneiana 15: 58-64.), occurring mainly in coastal areas of pantropical regions (Nelson 2008Nelson SC (2008) Cassytha filiformis. Plant Desease 42: 1-10.). |
Annual or perennial, hemiparasitic to holoparasitic vines, present in many habitats, ranging from coastal areas to high elevations, with sub-cosmopolitan distribution (Costea et al. 2015Costea M, García MA & Stefanović S (2015) A phylogenetically based infrageneric classification of the parasitic plant genus Cuscuta (Dodders, Convolvulaceae). Systematic Botany 40: 269-285.). |
Cuscuta species exhibit a range of plastome reductions (Braukmann et al. 2013Braukmann T, Kuzmina M & Stefanović S (2013) Plastid genome evolution across the genus Cuscuta (Convolvulaceae): two clades within subgenus Grammica exhibit extensive gene loss. Journal of Experimental Botany 64: 977-989.). |
| Stem morphology, micromorphology and anatomy |
Filiform, 0.4-3 mm thick with fine longitudinal rugae or ridges; glabrous or occasionally presenting trichomes, forming a puberulent indumentum cover; epidermis cuticle with waxy plaques; stomata numerous, in parallel rows; stomata guard cells at right angles with the longitudinal axis of the stems (Heide-Jørgensen 2008Heide-Jørgensen H (2008) Parasitic flowering plants. Brill.). Stem coils producing haustoria similar to the rest of the stem (Figs.1b,e; 2a-c). Anatomically, stems exhibit secondary growth and their wood has bordered pits with a torus; fibers develop in the phloem (Heide-Jørgensen 2008Heide-Jørgensen H (2008) Parasitic flowering plants. Brill.). |
Filiform, 0.3-2.4 mm thick, smooth and glabrous; epidermis cuticle without epicuticular deposits; stomata very few, irregularly distributed; stomata guard cells oriented in parallel with the longitudinal axis of stems (Yuncker 1943Yuncker TG (1943) Observations on the presence of stomata in some species of Cuscuta. Proceedings of the Indiana Academy of Science 53: 100-104.; Fig. 1j, k; Fig. 2d-e). Stem coils producing haustoria (haustorial stems) often develop multicellular projections with stomata, as in species of subg. Grammica (Fig. 2f-g) Stems lack secondary growth and fibers (wood is absent as well) (Clayson et al. 2014Clayson C, García-Ruiz I & Costea M (2014) Diversity, evolution, and function of stomata bearing structures in Cuscuta (dodders, Convolvulaceae): From extrafloral nectar secretion to transpiration in arid conditions. Perspectives in Plant Ecology, Evolution and Systematics 16: 310-321.). |
When broken, fresh stems of Cassytha are usually scented which is due to the presence of secretory tissues with essential oils (Weber 1981Weber JZ (1981) A taxonomic revision of Cassytha (Lauraceae) in Australia. Journal of the Adelaide Botanic Garden 3: 187-262., Tennakoon et al. 2016Tennakoon KU, Rosli R & Le QV (2016) Biology of aerial parasitic vines in Brunei Darussalam: Cuscuta and Cassytha. Scientia Bruneiana 15: 58-64.). Cuscuta stems have laticifers, but the latex secreted is inodorous (Clayson et al. 2014Clayson C, García-Ruiz I & Costea M (2014) Diversity, evolution, and function of stomata bearing structures in Cuscuta (dodders, Convolvulaceae): From extrafloral nectar secretion to transpiration in arid conditions. Perspectives in Plant Ecology, Evolution and Systematics 16: 310-321.). Dry stems of Cassytha are very rigid, while stems of Cuscuta are more flexible. |
| Stem color |
Generally greenish-olive but, occasionally becoming yellowish or orange (Fig. 1e-f,h). |
Yellowish, orange, reddish or purple, rarely greenish (Fig.1o-p). |
In both genera, stems become (dark) brown upon drying, but in Cuscuta they may preserve better their original yellowish-orange color (Fig.1j). |
| Leaves |
Alternate, reduced to inconspicuous scales, sessile, sometimes pubescent (Weber 1981Weber JZ (1981) A taxonomic revision of Cassytha (Lauraceae) in Australia. Journal of the Adelaide Botanic Garden 3: 187-262.). |
Alternate, reduced to microscopic scales, glabrous. |
Sometimes it is possible to observe the leaf scales of Cassytha at the stem apex. |
| Inflorescences |
Spikes, less frequently racemes or panicles (Weber 1981Weber JZ (1981) A taxonomic revision of Cassytha (Lauraceae) in Australia. Journal of the Adelaide Botanic Garden 3: 187-262., Kropf 2015); the few flowers widely spaced along the inflorescence axis (Fig.1a,e). |
Monochazial cymes (rarely thyrses), generally compound, dense and with numerous flowers (Fig.1j, l,p). |
Some Cuscuta species may have few-flowered inflorescences, in which case flower pedicels are usually conspicuous, while in Cassytha flowers are sessile or subsessile (Fig.1 e,h). |
| Flowers |
3-merous (Fig.1f-g); perianth elements free. |
4-5-merous (rarely 3-merous) (Fig.1m,o); perianth elements fused. |
Flowers are bisexual and radial in both genera. |
| Stamens |
9, arranged in 3 whorls; anthers open by two flaps (Fig.1f-g) |
4-5 on one cycle, alternating with the corolla lobes; anthers open by longitudinal slits (Fig.1o) |
As in other Convolvulaceae, the stamens of Cuscuta are fused with the corolla tube. |
| Staminodes |
Present in the 4th whorl. |
Staminodes absent. |
|
| Pollen |
Apolar; inaperturate; spheroidal, 25-60 mm in diameter, exine verrucate or spinuloid; (Van der Merwe et al. 1990Van der Merwe JJM, Van Wyk AE & Kok PDF (1990) Pollen types in the Lauraceae. Grana 29: 185-196.). |
Colpate, commonly 3(4)-zonocolpate, sometimes 5-6 (8)-colpate; prolate, spheroidal to oblate; 12-42 mm long; tectum imperforate to reticulate; exine with rounded or acute processes (Welsh et al. 2010Welsh M, Stefanović S, & Costea M (2010). Pollen evolution and its taxonomic significance in Cuscuta (dodders, Convolvulaceae). Plant Systematics and Evolution 285: 83-101.). |
Pollen grains in Cassytha are uniform while in Cuscuta they are polymorphic, variable as number of colpi within the same anther and flower. |
| Appendices |
A pair of glands is associated with the staminal filaments of the 3rd whorl (Weber 1981Weber JZ (1981) A taxonomic revision of Cassytha (Lauraceae) in Australia. Journal of the Adelaide Botanic Garden 3: 187-262.). |
Infra-staminal scales are associated with the base of staminal filaments, with great morphological diversity within the genus (Riviere et al. 2013Riviere S, Clayson C, Dockstader K, Wright MA & Costea M (2013) To attract or to repel? Diversity, evolution and role of the “most peculiar organ” in the Cuscuta flower (dodder, Convolvulaceae)—the infrastaminal scales. Plant Systematics and Evolution 299: 529-552.). |
In some species of Cuscuta, infra-staminal scales are completely reduced (e.g., Cuscuta grandiflora Kunth.; Riviere et al. 2013Riviere S, Clayson C, Dockstader K, Wright MA & Costea M (2013) To attract or to repel? Diversity, evolution and role of the “most peculiar organ” in the Cuscuta flower (dodder, Convolvulaceae)—the infrastaminal scales. Plant Systematics and Evolution 299: 529-552.). |
| Ovary |
Globose-elliptic, 1 locule with 1 ovule (Weber 1981Weber JZ (1981) A taxonomic revision of Cassytha (Lauraceae) in Australia. Journal of the Adelaide Botanic Garden 3: 187-262.). |
Globose, depressed-globose, ovoid or obovoid, 2 locules, 2 ovules per locule (Wright et al. 2011Wright MA, Welsh M & Costea M (2011) Diversity and evolution of the gynoecium in Cuscuta (dodders, Convolvulaceae) in relation to their reproductive biology: two styles are better than one. Plant Systematics and Evolution 296: 51-76.). |
Pollen/ovule ratios have been used to estimate breeding systems in Cuscuta (Wright et al. 2012Wright MA, Ianni MD & Costea M (2012). Diversity and evolution of pollen-ovule production in Cuscuta (dodders, Convolvulaceae) in relation to floral morphology. Plant Systematics and Evolution 298: 369-389.). |
| Style(s) |
1, terminal, conic (Fig.3c). |
1 or 2, terminal, cylindrical or subulate (Fig.3i). |
|
| Stigma |
1, narrow, inconspicuous (Endress & Igersheim 1997Endress PK & Igersheim A (1997) Gynoecium diversity and systematics of the Laurales. Botanical Journal of the Linnean Society 125: 93-168.). |
2, conspicuous, elongated, globose, flattened (other shapes are also possible, Wright et al. 2011Wright MA, Welsh M & Costea M (2011) Diversity and evolution of the gynoecium in Cuscuta (dodders, Convolvulaceae) in relation to their reproductive biology: two styles are better than one. Plant Systematics and Evolution 296: 51-76.). |
|
| Fruit |
Drupe, 4-10 x 3-7 mm (Fig.1a,d,i). |
Membranous capsule; dehiscent, indehiscent, or irregularly dehiscent (Ho & Costea 2018Ho A & Costea M (2018) Diversity, evolution and taxonomic significance of fruit in Cuscuta (dodder, Convolvulaceae); the evolutionary advantages of indehiscence. Perspectives in Plant Ecology, Evolution and Systematics 32: 1-17.) usually smaller than 0.5 cm (Fig.1n). |
In Cassytha, usually only a few fruits can be observed along the stems; Cuscuta often exhibits dense infructescences. |
| Seeds |
1 per fruit, glabrous; embryo not coiled, with 2 large cotyledons (Sastri 1962Sastri RLN (1962) Studies in Lauraceae. III. Embryology of Cassytha. Botanical Gazette 123: 197-206.). |
1-4 per fruit, glabrous, embryo filiform 1-4 times coiled; cotyledons absent Olszewski et al. (2020)Olszewski M, Dilliott M, García-Ruiz I, Bendarvandi B & Costea M (2020) Cuscuta seeds: diversity and evolution, value for systematics/identification and exploration of allometric relationships. PLOS One (accepted).. |
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