Balancing between reproductive and vegetative investment help maximize plants’ fitness and their long-term adaptation. This question can be interesting in a group of plants, ferns, that utilize the same organ, fronds, to carry out both reproductive and vegetative missions. Bearing sporangia for reproduction or not, fern fronds can be categorized as either fertile or sterile. In many ferns, two kinds of fronds are monomorphic in their appearance. By contrast, dimorphic fern species produce the two fronds in distinct morphologies. This dimorphism has long been assumed to enhance spore dispersal, but less attention looks deep into their reproductive investment at the organismal level. Our aim was to study (1) what foliar traits contribute most to the frond dimorphism of Tectaria ferns and (2) whether the degrees of frond dimorphism also correlate with their reproductive investment of spores. Nine Tectaria species with varied dimorphism levels were sampled, and size-independent parameters derived from quantitative foliar traits were used to infer the dimorphism degree through linear regression analysis (LDA). Leaf mass per area (LMA), spore production, and total mass of frond production were also calculated to estimate their annual spore production per foliar mass as their reproductive investment. We found that frond area and perimeter are the two main factors contributing to the dimorphism degree. A negative correlation was discovered between frond dimorphism and reproductive investment. The reproductive investment itself is size-dependent in most sampled species and rises as body size increases.