Vegetative Characters, Growth Habit and Microsporangiate Strobilus of Lycopsid Minostrobus chaohuensis

Abstract

Late Devonian Minostrobus chaohuensis is one of the earliest monosporangiate-strobilate isoetaleans. Based on new material of this plant, the vegetative axis and microsporangiate strobilus are studied in detail, and the whole plant knowledge is summarized. The vegetative axis is isotomously branched. The stem is up to 55 mm in diameter with helically arranged leaf cushions. Stems and thick branches bear long fusiform leaf cushions and interareas with vertical linear ornamentations. A ligule pit, oblanceolate leaf scar, and vascular bundle scar appear on the leaf cushion. Distal axes have persistent lanceolate leaves and rhombic leaf bases. The microsporangiate strobilus is cylindrical in shape, possesses sporophyll with alate pedicel and long triangular lamina, uniseriate sporangial wall, subarchesporial pad inside the sporangium, and microspore with cingulum. Based on comparisons with other isoetaleans, the usage of the terms “leaf cushion” and “leaf base” is discussed, and Minostrobus chaohuensis is considered as a tree-like lycopsid. It suggests that arborescent isoetaleans with monosporangiate strobili had appeared and diversified in the Late Devonian. The multi-dichotomous branching system of Minostrobus provides new data on the evolution of growth architecture in rhizomorphic lycopsids.

Kossoviella timanicaPetrosjan emend. from the Upper Devonian of North Timan: morphology and spore ultrastructure

“…2003; Wang et al 2003; Wang et al 2012; Meng et al . 2013, 2015, 2016; Wang et al 2014, 2016) appeared at this time, but only three of these (including Kossoviella ) were bisporangiate. Chamaedendron multisporangiatum from the Lower Frasnian of China (Schweitzer & Li 1996) is similar to Kossoviella in sporophyll morphology (crenulated margins and spoon-like base).…”

“…Minostrobus chaohuensis has been repeatedly reported from the Famennian of South China (Wang 2001; Wang et al 2012; Meng et al . 2013, 2015). The monosporangiate strobili of Minostrobus have sporangia that are similar in shape and size, and sporophylls that are similarly arranged on the axis.…”

“…2003; Wang et al 2012; Meng et al . 2013, 2015, 2016; Wang et al 2014, 2016). Finds of bisporangiate strobili and cone structures of early heterosporous lycopsids are very rare (Chitaley & McGregor 1988; Senkevitsch et al .…”

Lilingostrobus chaloneri gen. et sp. nov., a Late Devonian woody lycopsid from Hunan, China

“…Strobilate lycopsids diversified in the Late Devonian, and a large number of taxa are known. Representatives from China include the following genera: Changxingia [ 18 , 19 ], Lepidostrobus [ 20 ]; Leptophloeum [ 48 ], Minostrobus [ 21 – 24 ], Sublepidodendron [ 25 – 29 ], Wuxia [ 42 ]. The Late Devonian strobilate lycopsids had either bisporangiate strobili as in Bisporangiostrobus , from the Late Devonian of Pennsylvania [ 49 ] and Clevelandodendron , from the Late Devonian of Ohio [ 50 ] or monosporangiate strobili as in Lepidostrobus [ 20 ], Minostrobus [ 23 ] and Sublepidodendron [ 26 ].…”

“…This character evolved during Middle Devonian times in Longostachys [ 17 ], and preceded the acquisition of the “monosporangiate strobili” character that defines the Dichostrobiles. Only four Devonian genera with demonstrated monosporangiate strobili are known: Changxingia [ 18 , 19 ], Lepidostrobus [ 20 ], Minostrobus [ 21 – 24 ] and Sublepidodendron [ 25 – 29 ]. Interestingly, Sublepidodendron is the only unambiguous Devonian Dichostrobile, with demonstrated secondary xylem; the internal anatomy of the stem of Changxingia and Lepidostrobus is yet to be discovered, while only primary growth has been shown in Minostrobus [ 24 ].…”