John Booker

Program Director at SeaCamp /Newfound Harbor Marine Institute on Big Pine Key, FL

In Monroe County, three mangrove species dominate the wetland areas, the red mangrove (Rhizophora mangle), black mangrove (Avicennia germinans) and white mangrove (Laguncularia racemosa). The red mangrove is the tallest, with recorded heights of 25 m. The leaves are long (12 cm), waxy, dark green above and pale below. The broad leaves terminate with a blunt pointed apex. The roots, trunk and branches have a thin grey bark covering a dark red wood. Notable characteristics include the prop roots derived from the trunk and drop roots from aerial branches. Small yellow flowers are most common in the summer, but the long (15 cm), cigar shaped propagules may be found hanging on the tree at any time of the year.

The second tallest species in the Keys is the black mangrove, which may reach heights of 20 m. The small (10 cm) leaves are elliptical or oblong, and green on the upper surface. The undersurface is covered with dense hairs often encrusted with salt. The bark is dark and scaly. This tree displays distinctive aerial roots (pneumatophores), which stick up from the ground like thin fingers. Flowering occurs during summer months, and result in lima bean-shaped propagules (2-3 cm long) in late summer and early fall.

The white mangrove is the smallest of the three mangroves (sometimes it appears to be a shrub) with maximum heights of 15 m. It has broad, flat oval leaves up to 7 cm long that are rounded at both ends. Two salt glands are found at the base of each leaf at the apex of the petiole. Flowering occurs in mid to late summer and produces very small (<0.5 cm) propagules resembling peas a month later.

The buttonwood (Conocarpus erectus) is an associate of the mangrove community, but is more frequently found in the upland transitional zone. Its pointed leaves possess salt glands visible as openings alternating along the midrib on the underside of the leaf. Older trees display rough bark. Buttonwoods flower in the summer and produce a button-like seed case.

Monroe County weather is subtropical. Mangroves develop best in tropical climates (where the average temperature is greater than 19 deg. C), and for this reason, local mangroves tend to be smaller in size, have decreased leaf area and grow in denser communities than in tropical areas.