—157— Eleocharis ×myogiensis (Cyperaceae): A New Hybrid from Myoginohana Marsh, Lake Kasumigaura, Japan Katsuhiro Y ASHIRO * and Yasuhiko ENDO Graduate School of Science, Ibaraki University, 2-1-1, Bunkyo, Mito, Ibaraki, 310-8512 JAPAN *Corresponding author: [email protected] (Accepted on January 5, 2017) A new plant hybrid was identified in Myoginohana Marsh, Lake Kasumigaura, Ibaraki Prefecture, Japan, and named Eleocharis × myogiensis Yashiro (Cyperaceae). Its putative parents are E. petasata (Maxim.) Zinserl. and E. tsurumachii Ohwi. The hybrid has the floral and culm features intermediate between the putative parents, and a lower pollen stainability than that of the parents. Key words: Cyperaceae, Eleocharis × myogiensis, Eleocharis petasata, Eleocharis tsurumachii, Japan, Lake Kasumigaura, Myoginohana Marsh. J. Jpn. Bot. 92(3): 157–164 (2017) Myoginohana Marsh, in Inashiki-shi, Ibaraki Prefecture, occupies an area of approximately 52 ha located on the southwestern shores of Lake Kasumigaura (Nishiura)—the second largest lake in Japan. A total of 19 endangered plant species have been observed in the marsh, including Eleocharis tsurumachii Ohwi (Nozoe et al. 2010, Fujii 2015). In our preliminary study, one of us (Yashiro) found four distinct morphotypes of Eleocharis in Myoginohana Marsh. Three of them were E. petasata (Maxim.) Zinserl., E. tetraquetra Nees, and E. tsurumachii Ohwi, whereas the fourth morphotype was morphologically intermediate between E. petasata and E. tsurumachii . In the present study, we aimed to clarify whether the fourth morphotype was a hybrid between Eleocharis petasata and E. tsurumachii . Materials and Methods We examined 17 individuals of Eleocharis from Myoginohana Marsh, and the voucher specimens were deposited at the Ibaraki Nature Museum (INM), Bando, Ibaraki Prefecture, Japan (Table 1). The length of spikes, scales, achenes, and hypogynous bristles, as well as the width of culms were measured from dried herbarium specimens using a Peak scale loupe 7× (Tohkai Sangyo, Bunkyo-ku, Tokyo, Japan) (Table 1). The lengths of spinules on the bristles were measured using an ocular micrometer under a transverse light microscope. For the measurements, more than five organs from one individual were examined, e.g., the length of spikes is an average of more than five spikes of one individual. The culms of dried herbarium specimens were rehydrated by soaking in 5% aqueous KOH for 5 h (Lu et al. 2004, Both et al. 2009), washed with water, and then deposited in 70% aqueous ethanol. The rehydrated culms were manually sectioned into approximately 0.2 mm thick slices, using a razor blade. These sections were stained with aqueous safranin and observed under a transverse light microscope to count the number of vascular bundles and ridges at the