## 2 Lignocellulose Feedstock Biorefineries
### Low-Input Crops: Sources and Availability
#### 2.3.3 Cup Plants: Silphium Perfoliatum  
Unlike _Miscanthus_, _Silphium perfoliatum_ L. belongs to the class of perennial C\({}_{3}\) plants, with characteristic yellow flowers (Figure 6). Originally, it was cultivated in North America and then brought to Europe in the 18 th century. Currently, _Silphium_ crops are established and distributed all over the world, including North and South America (Chile, USA), Asia (China, Japan), and Europe (France, Switzerland, Romania, Czech Republic, Germany, Hungary, Poland, Austria, Russia), with the plants mainly being investigated as a raw material for biogas, biofuel, and chemical production. The  
Figure 5: _Paulownia_ tree cultivated at the Campus Klein-Altendorf, Germany. Copyright 2019, [PERSON]. advantages of these plants as a raw material are the low maintenance requirements, optimal growth (even in arid conditions), and high yields (Figure 6) [115; 116; 117]. _Silphin_ crops are discussed as promising candidates for biogas production. According to [PERSON] et al., the annual harvest yield can reach about 10 to 15 t per ha. Compared to maize, the biomethane production is 20% lower. However, so far there are a very limited number of studies and a lot of questions to be answered regarding the potential of these plants as lignocellulosic feedstock. Thus, a seed technology must be developed, pathogen susceptibility has to be checked, and a suitable herbicide for weed management during the first cultivation year is most probably required [118]. The Lithuanian Research Centre for Agriculture and Forestry in Western Lithuania performed a field study reported by [PERSON] and colleagues--the authors cultivated various perennial coarse-stemmed herbaceous energy plants, including mugwort (_Arteniisia vulgaris_ L.) and cup plant (_Silplium perfoliatum_ L.). For their field trial, the authors used a two-factor design, including three levels of liming (not limed versus lined, using CaCO\({}_{3}\) in different concentrations) and nitrogen as the fertilizer in varying concentrations, to study the influence of these parameters on the cup plant dry matter productivity. Results showed that both fertilizer and lime significantly influence (decrease) the energy output and energy use efficiency [119]. So far, _Silplium perfoliatum_ L. has been studied in detail regarding its utilization as an additive for food and pharmaceuticals and as raw materials for bioenergy and biofuel production [119; 120]. In another study, [PERSON] and colleagues investigated the exploitation of agricultural crop residues as renewable sources for particleboard production. The following samples were studied: cup-plant (_Silplium perfoliatum_ L.), sunflower (_Helianthusannus_ L.), and topinambour (_Helianthus tuberosus_ L.). Particleboards of 600 kg/m\({}^{3}\) density were produced using different adhesives (methylene diphenyl diisocyanate, urea formaldehyde resin). Various physical and mechanical properties of the final boards were measured, including rupture modulus, thickness, swelling, and water absorption. Based on the obtained data, the authors concluded that agricultural crop residues can be used for particleboard and furniture production, meeting European standard EN 312 class P1 [121]. [PERSON] et al. studied the exploitation of sunflower stalks as an alternative raw material for particleboards. As a pretreatment method, acetylation was conducted, to increase the thickness swelling (TS) of the boards. Thus, up to 19.7% weight gain could be obtained. Unfortunately, the introduction of acetyl functionalities resulted in a decrease in the internal bond strength. The authors concluded that a mixture of industrial wood chips and sunflower stalks might be appropriate to improve the particleboard specifications [122]. Figure 6: **Left**: _Silphin perfoliatum_ L. **(a)** quadrangular stalk, **(b)** cup-shaped leaf axil, **(c)** branched stalk with flower buds and flower heads, **(d)** flower head with tubular and ligulate ray flowers, **(e)** mature inflorescence, and **(f)** fruits.