Degradation of lignified tissues in leaf blades and stems and reduction in textural strength of stems of bermuda grass by axenic cultures of ruminal fungi was investigated. Fungal isolates were evaluated that demonstrated monocentric growth ( Piromyces MC-1 and Neocallimastix MC-2) or polycentric growth (unnamed PC-1 and Orpinomyces PC-2 and PC-3). In in vitro digestion studies over a period of 9 days, all isolates eventually degraded ∼ 70% of the leaf dry matter, but the rate of digestion varied from fastest to slowest as follows: MC-2 > PC-2, PC-3 > PC-1 > MC-1. For stems, all isolates except MC-1 degraded about the same amount of dry matter (∼ 45%) with following order of fastest to slowest: PC-3 > PC-2 > MC-2 > PC1 > MC-1. Isolate MC-1 did not grow well on bermuda-grass stems. The reduction in textural strength of bermuda grass stems after incubation with ruminal fungi was similar for all isolates (∼ 45%) except MC-1. All polycentric isolates reduced the strength of stems at a faster rate than the monocentric ones, with PC-3 the fastest of all cultures. Specific activities for enzymes involved in degradation of stems (cellulase, xylanase, β-glucosidase, and β-xylosidase) increased with time of incubation. PC-3 produced the highest activities and PC-1 the lowest (MC-1 was not tested as it grew poorly on stems). Ultrastructural studies of plant cell wall degradation by fungal isolates showed that they all had the ability to degrade the most limiting structural barrier to digestion (i.e. xylem and mestome sheath in leaves and sclerenchyma ring in stems), and could disrupt and penetrate the cuticular barrier of the leaves. The ability of anaerobic fungi to fully or partially degrade the most recalcitrant tissues to digestion resulted in a residue that would likely be more easily broken down by subsequent chewing by ruminants, thus possibly contributing to enhanced fiber flow. Substantial variations existed among fungal isolates in their ability to degrade and weaken fiber, and future work to enhance lignocellulose utilization should take into account such variations.