Cuscuta seeds: Diversity and evolution, value for systematics/identification and exploration of allometric relationships

Abstract

Cuscuta (dodders) is a group of parasitic plants with tremendous economic and ecological significance. Their seeds are often described as "simple" or "unspecialized" because they do not exhibit any classical dispersal syndrome traits. Previous studies of seed morphology and/or anatomy were conducted on relatively few species. We expanded research to 101 species; reconstructed ancestral character states; investigated correlations among seed characters and explored allometric relationships with breeding systems, the size of geographical distribution of species in North America, as well as the survival of seedlings. Seed morphological and anatomical characters permit the separation of subgenera, but not of sections. Identification of Cuscuta species using seed characteristics is difficult but not impossible if their geographical origin is known. Seeds of subg. Monogynella species, exhibit the likely ancestral epidermis type consisting of elongated and interlocked cells, which are morphologically invariant, uninfluenced by dryness/wetness. Subgenera Cuscuta, Pachystigma and Grammica have evolved a seed epidermis with isodiametric cells that can alternate their morphology between two states: pitted when seeds are dry, and papillose after seed imbibition. A seed coat with double palisade architecture throughout the entire seed has also apparently evolved in subgenera Cuscuta, Pachystigma and Grammica, but several species in two clades of the latter subgenus reverted to a single palisade layer outside the hilum area. The same latter species also evolved a peculiar, globose embryo, likely having a storage role, in contrast to the ancestral filiform and coiled embryo present throughout the remainder of the genus. Autogamous species had on average the highest number of seeds per capsule, whereas fully xenogamous taxa had the lowest. No correlation was revealed between the size of the seeds and the size of their geographical distribution in North America, but seedlings of species with larger seeds survived significantly longer than seedlings resulted from smaller seeds. Diversity and evolution of seed traits was discussed in relationship with their putative roles in dormancy, germination and dispersal.

Comparative phylogeographic analysis of Cuscuta campestris and Cuscuta reflexa in Kenya: Implications for management of highly invasive vines

“…We also speculate that C. campestris , a naturalized invader, could be predominantly propagating through seed, hence enhanced mixing among populations, whereas C. reflexa may be largely spreading via vines although this remains to be confirmed. C. reflexa has larger seeds than C. campestris , although previous researchers found no evidence of any association between seed size and geographical distribution range among members of the genus Cuscuta (Olszewski et al, 2020). Future investigations are expected to elucidate the relationship between reproductive plasticity and the observed genetic variability in Cuscuta spp.…”

New records of Cuscuta L. (Convolvulaceae) in Central-West Brazil

“…Cuscuta xanthochortos occurs mainly in regions having a subtropical climate, and the new record of this species in the tropical Central-Western region of Brazil (which has a tropical climate) was found in an urban garden, where the species was likely introduced (Olszewski et al 2020). The new record of C. platyloba suggests that this species probably occurs throughout the Brazilian territory; however, as with other Cuscuta species, there has been underreporting of occurrences.…”

“…However, Cuscuta is currently included in the family Convolvulaceae based on molecular phylogenetic studies that have shown the genus is nested within the morning glories family (Stefanovic et al 2002;Stefanovic and Olmstead 2004). Also, Cuscuta has strong affinities with Convolvulaceae based on their flowers (Wright et al 2011(Wright et al , 2012, fruits (Ho and Costea 2018), and seeds (Olszewski et al 2020). Yuncker (1932) conducted a worldwide taxonomic revision of Cuscuta, providing an infrageneric classification as well as descriptions and illustrations for all the species.…”

Parasitism-evoked horizontal gene transfer between plants as a novel trigger for specialized metabolism evolution

“…One such role might be to prevent lipid peroxidation by exerting their (pro)antioxidative activities 33 , thereby preserving storage resources in oil bodies for biogenesis in the next generation. This trait conferred by seed lignans seems also to be bene cial for survival of Cuscuta seedlings, which entirely rely on the nutritive reserves stored in the endosperm until they start sucking nutrition from host plants via haustoria 50 . Furthermore, a sterol-binding dehydrogenase found in oil bodies, known as steroleosin (Sol), is widespread in seed plants including gymnosperms, and is involved in germination and development by regulating phytohormone sensitivity 51,52 .…”