First report of the parasitic invasive weed field dodder () parasitizing the confamilial invasive weed common morning-glory () in Shandong, China.

Common morning-glory ( (L.) Roth, Convolvulaceae), an annual herbaceous vine native to South America, was first recorded to be cultivated in China in 1890, and since then it has invaded all provinces of China. It was one of the 18 alien invasive species in China (MEE. 2014). As an invasive weed, it can readily invade dry lands, orchards, and nurseries and compete for sunlight by wrapping other plants. On 20 September 2019 and 18 July 2020, was found to be parasitized by a dodder species (also Convolvulaceae) in Lushan Mountain (36°21'N, 118°3'E, 569 m elevation), Shandong province, China (Fig. S1). Within and area of ca. 100 m, dozens of individuals of common morning-glory were parasitized by the leafless stems of dodder. After removal of the haustrial connection of the dodder stem from the stem, brownish black lesions around uneven holes were visible on the stem, with broken haustoria clearly visible to our naked eye remaining in the stem (Fig. S1). Anatomical results showed that the haustoria of dodder penetrate stem and xylem elements connect the vascular systems of both the parasitic and host plant (Fig. S1). Based on morphological characteristics of stems, inflorescences, calyx, corolla, stamens, and capsules as described in Costea et al. (2006), this dodder was identified as Yunck. (i.e., field dodder). Field dodder is readily distinguished from and in China by the capsules with persistent corollas enveloping 1/3 or less of its base and the spreading and inflexed corolla lobes with acute to acuminate apices. In order to further confirm the identity of the species, total genomic DNA was extracted and sequenced using genome-skimming method as described in Qu et al. (2019). An 831-bp region of 18S-ITS1-5.8S-ITS2-26S for the dodder studied was assembled, examined, and deposited in GenBank under accession number MN718805. The new sequence has 100% similarity with other available sequences of (accession number: KT383104, KT383150, KY968857). Phylogenetic analysis also placed the new dodder accession with other accessions of (Fig. S2a). In addition, the plastome sequence of the dodder studied was assembled (86,727 bp in length) and deposited in GenBank under accession number MN708214, and a BLAST analysis found that it was 99.98% similar to that of (accession number: AM711639). The plastome of was published by Funk et al. (2007). However, Costea et al. (2015) indicated that Funk et al. (2007) misidentified as . Furthermore, our phylogenetic tree strongly supported the identification of the dodder studied as (Fig. S2b). Therefore, the dodder on common morning-glory in Shandong province was finally identified as according to morphological and molecular evidence. The specimen of on was deposited at the herbarium of the College of Life Sciences, Shandong Normal University (voucher number: 092012B). Field dodder, the second most common dodder species in North America, is the most widespread weed in the world and has been found in Africa, Asia, Australia, Europe, and South America (Holm et al. 1997). To our knowledge, this is the first report of the parasitic invasive weed parasitizing the invasive weed in Shandong of China. This is also the first report of species parasitizing confamilial species, which is especially noteworthy given that the genus is sister to the genus . This study provides a good model for exploring gene flow between species of closely related genera with different lifestyle. Another implication of this study is that customs and departments of inspection and quarantine need to quarantine the seeds or plants of both dodders and common morning-glories.