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Senna cardiosperma – Fabaceae
Because of the considerable variation of Senna spp., plus their tendency to readily hybridise, these plants are often very tricky to identify as many past classification attempts can testify. However, Senna cardiosperma is one of the more obvious due to their compressed foliage arrangement. The leaflets can number between 2 and 14 pairs, although around Esperance they are usually 3 or 4 pairs. The important feature is the leaflets are less than 5 mm apart and less than 15 mm (5/8”) in length. Consequently they are tightly spaced along the rachis (stalk), but if the spacings or leaflet size is greater (locally not uncommon), they are either a different species or a hybrid.
Senna cardiosperma is an inland species and common in the Kalgoorlie region. Around Esperance it occurs in the mallee, arcing 100 km (over 60 miles) NW to the NE of the town and becoming more common the further north you go. Like other Senna spp. it germinates readily in a variety of well-drained soils after bushfire or soil disturbance and can grow to around 2 metres (6’) in height, although plants are usually shorter and quite bushy.
The flowers tend to be distinctly yellow when growing in a sandy loam over limestone, but develop an orange tinge when over gravel. Senna cardiosperma is a prolific producer of flowers that are shown to advantage by easily exceeding the squat compressed foliage near the stem. Flowering times locally are usually between July and November, but can also bloom later if local rainfall is drenching and temperatures mild.