| Life form |
Perennial, hemiparasitic vines (Heide-Jørgensen 2008, Tennakoon et al. 2016), occurring mainly in coastal areas of pantropical regions (Nelson 2008). |
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. 2015). |
Cuscuta species exhibit a range of plastome reductions (Braukmann et al. 2013). |
| 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 2008). 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 2008). |
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 1943; 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. 2014). |
When broken, fresh stems of Cassytha are usually scented which is due to the presence of secretory tissues with essential oils (Weber 1981, Tennakoon et al. 2016). Cuscuta stems have laticifers, but the latex secreted is inodorous (Clayson et al. 2014). 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 1981). |
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 1981, 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. 1990). |
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. 2010). |
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 1981). |
Infra-staminal scales are associated with the base of staminal filaments, with great morphological diversity within the genus (Riviere et al. 2013). |
In some species of Cuscuta, infra-staminal scales are completely reduced (e.g., Cuscuta grandiflora Kunth.; Riviere et al. 2013). |
| Ovary |
Globose-elliptic, 1 locule with 1 ovule (Weber 1981). |
Globose, depressed-globose, ovoid or obovoid, 2 locules, 2 ovules per locule (Wright et al. 2011). |
Pollen/ovule ratios have been used to estimate breeding systems in Cuscuta (Wright et al. 2012). |
| Style(s) |
1, terminal, conic (Fig.3c). |
1 or 2, terminal, cylindrical or subulate (Fig.3i). |
|
| Stigma |
1, narrow, inconspicuous (Endress & Igersheim 1997). |
2, conspicuous, elongated, globose, flattened (other shapes are also possible, Wright et al. 2011). |
|
| Fruit |
Drupe, 4-10 x 3-7 mm (Fig.1a,d,i). |
Membranous capsule; dehiscent, indehiscent, or irregularly dehiscent (Ho & Costea 2018) 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 1962). |
1-4 per fruit, glabrous, embryo filiform 1-4 times coiled; cotyledons absent Olszewski et al. (2020). |
|
Disentangling parasitic vines in the tropics: taxonomic notes for an accurate identification of Cuscuta (Convolvulaceae) and Cassytha (Lauraceae)
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