Cryptophyllium

Several species were previously placed in the genus Phyllium (subgenus Phyllium), which is very similar. Females of Cryptophyllium typically have antennae with short and disk-like fourth segments which are at least three times wider than they are long, and shorter than any of the following three segments. In Phyllium, the fourth antennal segment is as tall as it is wide and is of a similar height to each of the following three segments' length. Cryptophillium females are 77–107 mm long and males are about 55–89 mm.^[2]

The distribution area of the genus Cryptophyllium extends eastward to Sri Lanka. In the north, it ranges from Nepal through the Indian states of West Bengal and Assam, the Chinese Tibet Autonomous Region, to the province of Yunnan. In the east, the distribution area extends from the Chinese autonomous region of Guangxi through Hainan Province to the distant Micronesian island of Yap. The southern limit of the genus's distribution includes Sumatra, Bangka Island, Sulawesi, and Peleng, reaching its southernmost point at Buton Island and Wangi-wangi Island, located southeast of Sulawesi. Within these boundaries, most species have been described from Vietnam. Further species have been recorded from Myanmar, Laos, Cambodia, and Singapore, as well as the Malay Peninsula and Borneo. Due to Bhutan's location amidst Nepal, Tibet, and Assam, Cryptophyllium is also assumed to occur there. Unidentified or undescribed species of the genus have also been observed in the Andaman Islands and on the Philippine islands of Cebu and Mindanao, specifically on the Zamboanga Peninsula.^[1][2]

Frank H. Hennemann et al. proposed in 2009 the division of the genus Phyllium and its then subgenera into species groups. They placed Phyllium (Phyllium) celebicum, described in 1842 by Wilhem de Haan, together with Phyllium (Phyllium) athanysus, Phyllium (Phyllium) parum, Phyllium (Phyllium) rarum, Phyllium (Phyllium) tibetense, Phyllium (Phyllium) westwoodii and Phyllium (Phyllium) yunnanense, as well as the newly described Phyllium (Phyllium) ericoriai, in the Celebicum species group. The main characteristic of this group is the presence of hindwings in the females of these species.^[5] With the exception of Phyllium ericoriai, the seven other species, along with three additional species described between 2009 and 2021, were transferred in 2021 to the genus Cryptophyllium, established by Royce T. Cumming, Sarah Bank, Joachim Bresseel, Jérôme Constant, Stéphane Le Tirant, Zhiwei Dong, Gontran Sonet, and Sven Bradler. Phyllium drunganum, previously classified by Hennemann et al. in the Siccifolium species group, was also transferred to this genus. The fact that the only known specimen at the time, the female holotype, also possessed long hindwings was not known then. Cumming et al. described 13 further species concurrently with the establishment of the genus Cryptophyllium. The earliest described species, Cryptophyllium celebicum, was designated as the type species.^[1][2]

The name "Cryptophyllium" means "hidden leaf" or "secret leaf" and is composed of the Latinized name Phyllium, the type genus of the family (from the Greek φυλλον, -ου (phyllon, -oy)), and the prefix "Crypto", Latinized from the Ancient Greek word κρύπτο (krypto) for "hidden", "concealed", or "secret". Like Phyllium, Cryptoiphyllium is also neuter.

The genus Cryptophyllium currently comprises the following 24 species:^[1][2]

• Cryptophyllium animatum Cumming, Bank, Bresseel, Constant, Le Tirant, Dong, Sonet & Bradler, 2021 - Vietnam
• Cryptophyllium athanysus (Westwood, 1859) - Sri Lanka
• Cryptophyllium bankoi Cumming et al., 2021 - Vietnam
• Cryptophyllium bollensi Cumming et al., 2021 - Vietnam
• Cryptophyllium celebicum (de Haan, 1842) – type species (as Phyllium celebicum de Haan, 1842) - Sulawesi
• Cryptophyllium chrisangi (Seow-Choen, 2017) - Thailand, Malay Peninsula, Singapore, Sumatra & Borneo
• Cryptophyllium daparo Cumming et al., 2021 - China (Yunnan)
• Cryptophyllium drunganum (Yang, 1995) - China (Yunnan)
• Cryptophyllium echidna Cumming et al., 2021 - Sulawesi
• Cryptophyllium faulkneri Cumming et al., 2021 - Vietnam
• Cryptophyllium icarus Cumming et al., 2021 - Vietnam
• Cryptophyllium khmer Cumming et al., 2021 - Cambodia
• Cryptophyllium limogesi Cumming et al., 2021 - Vietnam
• Cryptophyllium liyananae Cumming et al., 2021 - China (Guangxi)
• Cryptophyllium nuichuaense Cumming et al., 2021 - Vietnam
• Cryptophyllium oyae (Cumming & Le Tirant, 2020) - Thailand, Laos & China (Yunnan)
• Cryptophyllium parum (Liu, 1993) - China (Hainan & Guangdong)
• Cryptophyllium phami Cumming et al., 2021 - Vietnam
• Cryptophyllium rarum (Liu, 1993) - China (Guangxi)
• Cryptophyllium tibetense (Liu, 1993) - Nepal, China (Tibet) & India (West Bengal & Assam)
• Cryptophyllium wennae Cumming et al., 2021 - China (Yunnan)
• Cryptophyllium westwoodii (Wood-Mason, 1875) - Thailand, Laos & Myanmar
• Cryptophyllium yapicum (Cumming & Teemsma, 2018) - Mikronesia (Yap Island)
• Cryptophyllium yunnanense (Liu, 1993) - China (Yunnan)

Bank et al., in their 2021 publication on phylogeny and historical biogeography, examined samples of various leaf insects using molecular genetics. These included 19 species from the genus Cryptophyllium. Based on the results of these investigations, Cryptophyllium is the sister genus of a clade consisting of the genera Phyllium, Pulchriphyllium, Microphyllium, and Pseudomicrophyllium.^[3] Another molecular genetic classification of the genus, which excludes the genera Acentetaphyllium, Rakaphyllium, and Vaabonbonphyllium, also showed that Microphyllium and Pseudomicrophyllium are the sister genera of Pulchriphyllium and that these form a common clade with Cryptophyllium. The next higher clade includes the genus Phyllium (see also Cladogram of the Phylliidae).^[4]